Attachment 8492591 Details for Bug 907396

[patch] Frame constructor changes for display:contents.

907396-display-contents-Fctor (text/plain), 47.47 KB, created by Mats Palmgren (inactive)

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Creator: Mats Palmgren (inactive)

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patch

obsolete

># HG changeset patch
># Parent af86ae864ba0acc6bca1bb62424ae5655cd18910
># User Mats Palmgren <matspal@gmail.com>
>Bug 907396 - Frame constructor changes for display:contents.  r=bzbarsky
>
>diff --git a/layout/base/RestyleManager.cpp b/layout/base/RestyleManager.cpp
>--- a/layout/base/RestyleManager.cpp
>+++ b/layout/base/RestyleManager.cpp
>@@ -3522,9 +3522,41 @@ RestyleManager::ComputeStyleChangeFor(ns
>         NS_ASSERTION(!cont->GetPrevContinuation(),
>                      "continuing frame had more severe impact than first-in-flow");
>         return;
>       }
>     }
>   }
> }
> 
>+AutoDisplayContentsAncestorPusher::AutoDisplayContentsAncestorPusher(
>+  TreeMatchContext& aTreeMatchContext, nsPresContext* aPresContext,
>+  nsIContent* aParent)
>+  : mTreeMatchContext(aTreeMatchContext)
>+  , mPresContext(aPresContext)
>+{
>+  if (aParent && mTreeMatchContext.mAncestorFilter.HasFilter()) {
>+    nsFrameManager* fm = mPresContext->FrameManager();
>+    // Push display:contents mAncestors onto mTreeMatchContext.
>+    for (nsIContent* p = aParent; p && fm->GetDisplayContentsStyleFor(p);
>+         p = p->GetParent()) {
>+      mAncestors.AppendElement(p->AsElement());
>+    }
>+    nsTArray<mozilla::dom::Element*>::size_type i = mAncestors.Length();
>+    while (i--) {
>+      mTreeMatchContext.mAncestorFilter.PushAncestor(mAncestors[i]);
>+      mTreeMatchContext.PushStyleScope(mAncestors[i]);
>+    }
>+  }
>+
>+}
>+
>+AutoDisplayContentsAncestorPusher::~AutoDisplayContentsAncestorPusher()
>+{
>+  // Pop the ancestors we pushed in the CTOR, if any.
>+  nsTArray<mozilla::dom::Element*>::size_type i = mAncestors.Length();
>+  while (i--) {
>+    mTreeMatchContext.mAncestorFilter.PopAncestor();
>+    mTreeMatchContext.PopStyleScope(mAncestors[i]);
>+  }
>+}
>+
> } // namespace mozilla
>diff --git a/layout/base/RestyleManager.h b/layout/base/RestyleManager.h
>--- a/layout/base/RestyleManager.h
>+++ b/layout/base/RestyleManager.h
>@@ -25,17 +25,18 @@ struct TreeMatchContext;
> 
> namespace mozilla {
>   class EventStates;
> 
> namespace dom {
>   class Element;
> } // namespace dom
> 
>-class RestyleManager MOZ_FINAL {
>+class RestyleManager MOZ_FINAL
>+{
> public:
>   friend class ::nsRefreshDriver;
>   friend class RestyleTracker;
> 
>   typedef mozilla::dom::Element Element;
> 
>   explicit RestyleManager(nsPresContext* aPresContext);
> 
>@@ -394,17 +395,18 @@ private:
>   RestyleTracker mPendingRestyles;
>   RestyleTracker mPendingAnimationRestyles;
> };
> 
> /**
>  * An ElementRestyler is created for *each* element in a subtree that we
>  * recompute styles for.
>  */
>-class ElementRestyler MOZ_FINAL {
>+class ElementRestyler MOZ_FINAL
>+{
> public:
>   typedef mozilla::dom::Element Element;
> 
>   // Construct for the root of the subtree that we're restyling.
>   ElementRestyler(nsPresContext* aPresContext,
>                   nsIFrame* aFrame,
>                   nsStyleChangeList* aChangeList,
>                   nsChangeHint aHintsHandledByAncestors,
>@@ -544,11 +546,32 @@ private:
>   const DesiredA11yNotifications mDesiredA11yNotifications;
>   DesiredA11yNotifications mKidsDesiredA11yNotifications;
>   A11yNotificationType mOurA11yNotification;
>   nsTArray<nsIContent*>& mVisibleKidsOfHiddenElement;
>   bool mWasFrameVisible;
> #endif
> };
> 
>+/**
>+ * This pushes any display:contents nodes onto a TreeMatchContext.
>+ * Use it before resolving style for kids of aParent where aParent
>+ * (and further ancestors) may be display:contents nodes which have
>+ * not yet been pushed onto TreeMatchContext.
>+ */
>+class MOZ_STACK_CLASS AutoDisplayContentsAncestorPusher MOZ_FINAL
>+{
>+ public:
>+  typedef mozilla::dom::Element Element;
>+  AutoDisplayContentsAncestorPusher(TreeMatchContext& aTreeMatchContext,
>+                                    nsPresContext*    aPresContext,
>+                                    nsIContent*       aParent);
>+  ~AutoDisplayContentsAncestorPusher();
>+  bool IsEmpty() const { return mAncestors.Length() == 0; }
>+private:
>+  TreeMatchContext& mTreeMatchContext;
>+  nsPresContext* const mPresContext;
>+  nsAutoTArray<mozilla::dom::Element*, 4> mAncestors;
>+};
>+
> } // namespace mozilla
> 
> #endif /* mozilla_RestyleManager_h */
>diff --git a/layout/base/RestyleTracker.cpp b/layout/base/RestyleTracker.cpp
>--- a/layout/base/RestyleTracker.cpp
>+++ b/layout/base/RestyleTracker.cpp
>@@ -4,19 +4,22 @@
>  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
> 
> /**
>  * A class which manages pending restyles.  This handles keeping track
>  * of what nodes restyles need to happen on and so forth.
>  */
> 
> #include "RestyleTracker.h"
>+
>+#include "GeckoProfiler.h"
>+#include "nsFrameManager.h"
>+#include "nsIDocument.h"
> #include "nsStyleChangeList.h"
> #include "RestyleManager.h"
>-#include "GeckoProfiler.h"
> 
> namespace mozilla {
> 
> inline nsIDocument*
> RestyleTracker::Document() const {
>   return mRestyleManager->PresContext()->Document();
> }
> 
>@@ -74,18 +77,20 @@ CollectRestyles(nsISupports* aElement,
>   if (element->GetCrossShadowCurrentDoc() != collector->tracker->Document() ||
>       !element->HasFlag(collector->tracker->RestyleBit())) {
>     return PL_DHASH_NEXT;
>   }
> 
>   NS_ASSERTION(!element->HasFlag(collector->tracker->RootBit()) ||
>                // Maybe we're just not reachable via the frame tree?
>                (element->GetFlattenedTreeParent() &&
>-                (!element->GetFlattenedTreeParent()->GetPrimaryFrame()||
>-                 element->GetFlattenedTreeParent()->GetPrimaryFrame()->IsLeaf())) ||
>+                (!element->GetFlattenedTreeParent()->GetPrimaryFrame() ||
>+                 element->GetFlattenedTreeParent()->GetPrimaryFrame()->IsLeaf() ||
>+                 element->GetCurrentDoc()->GetShell()->FrameManager()
>+                   ->GetDisplayContentsStyleFor(element))) ||
>                // Or not reachable due to an async reinsert we have
>                // pending?  If so, we'll have a reframe hint around.
>                // That incidentally makes it safe that we still have
>                // the bit, since any descendants that didn't get added
>                // to the roots list because we had the bits will be
>                // completely restyled in a moment.
>                (aData->mChangeHint & nsChangeHint_ReconstructFrame),
>                "Why did this not get handled while processing mRestyleRoots?");
>diff --git a/layout/base/nsCSSFrameConstructor.cpp b/layout/base/nsCSSFrameConstructor.cpp
>--- a/layout/base/nsCSSFrameConstructor.cpp
>+++ b/layout/base/nsCSSFrameConstructor.cpp
>@@ -606,40 +606,16 @@ FindFirstNonBlock(const nsFrameList& aLi
> inline void
> SetInitialSingleChild(nsContainerFrame* aParent, nsIFrame* aFrame)
> {
>   NS_PRECONDITION(!aFrame->GetNextSibling(), "Should be using a frame list");
>   nsFrameList temp(aFrame, aFrame);
>   aParent->SetInitialChildList(kPrincipalList, temp);
> }
> 
>-static nsContainerFrame*
>-GetContentInsertionFrameFor(nsIContent* aContent)
>-{
>-  // Get the primary frame associated with the content
>-  nsIFrame* frame = aContent->GetPrimaryFrame();
>-
>-  if (!frame)
>-    return nullptr;
>-
>-  // If the content of the frame is not the desired content then this is not
>-  // really a frame for the desired content.
>-  // XXX This check is needed due to bug 135040. Remove it once that's fixed.
>-  if (frame->GetContent() != aContent) {
>-    return nullptr;
>-  }
>-
>-  nsContainerFrame* insertionFrame = frame->GetContentInsertionFrame();
>-
>-  NS_ASSERTION(!insertionFrame || insertionFrame == frame || !frame->IsLeaf(),
>-    "The insertion frame is the primary frame or the primary frame isn't a leaf");
>-
>-  return insertionFrame;
>-}
>-
> // -----------------------------------------------------------
> 
> // Structure used when constructing formatting object trees.
> struct nsFrameItems : public nsFrameList
> {
>   // Appends the frame to the end of the list
>   void AddChild(nsIFrame* aChild);
> };
>@@ -2283,18 +2259,19 @@ NeedFrameFor(const nsFrameConstructorSta
>   // whitespace.
> 
>   // We could handle all this in CreateNeededPseudos or some other place
>   // after we build our frame construction items, but that would involve
>   // creating frame construction items for whitespace kids of
>   // eExcludesIgnorableWhitespace frames, where we know we'll be dropping them
>   // all anyway, and involve an extra walk down the frame construction item
>   // list.
>-  if (!aParentFrame->IsFrameOfType(nsIFrame::eExcludesIgnorableWhitespace) ||
>-      aParentFrame->IsGeneratedContentFrame() ||
>+  if ((aParentFrame &&
>+       (!aParentFrame->IsFrameOfType(nsIFrame::eExcludesIgnorableWhitespace) ||
>+        aParentFrame->IsGeneratedContentFrame())) ||
>       !aChildContent->IsNodeOfType(nsINode::eTEXT)) {
>     return true;
>   }
> 
>   aChildContent->SetFlags(NS_CREATE_FRAME_IF_NON_WHITESPACE |
>                           NS_REFRAME_IF_WHITESPACE);
>   return !aChildContent->TextIsOnlyWhitespace();
> }
>@@ -2583,17 +2560,18 @@ nsCSSFrameConstructor::ConstructDocEleme
>     // if the document is a table then just populate it.
>     contentFrame = static_cast<nsContainerFrame*>(
>       ConstructTable(state, item, mDocElementContainingBlock,
>                      styleContext->StyleDisplay(),
>                      frameItems));
>     newFrame = frameItems.FirstChild();
>     NS_ASSERTION(frameItems.OnlyChild(), "multiple root element frames");
>   } else {
>-    MOZ_ASSERT(display->mDisplay == NS_STYLE_DISPLAY_BLOCK,
>+    MOZ_ASSERT(display->mDisplay == NS_STYLE_DISPLAY_BLOCK ||
>+               display->mDisplay == NS_STYLE_DISPLAY_CONTENTS,
>                "Unhandled display type for root element");
>     contentFrame = NS_NewBlockFormattingContext(mPresShell, styleContext);
>     nsFrameItems frameItems;
>     // Use a null PendingBinding, since our binding is not in fact pending.
>     ConstructBlock(state, display, aDocElement,
>                    state.GetGeometricParent(display,
>                                             mDocElementContainingBlock),
>                    mDocElementContainingBlock, styleContext,
>@@ -3690,29 +3668,31 @@ nsCSSFrameConstructor::ConstructFrameFro
> 
>   // Don't create a subdocument frame for iframes if we're creating extra frames
>   if (aState.mCreatingExtraFrames && aItem.mContent->IsHTML() &&
>       aItem.mContent->Tag() == nsGkAtoms::iframe)
>   {
>     return;
>   }
> 
>-  nsStyleContext* const styleContext = aItem.mStyleContext;
>-  const nsStyleDisplay* display = styleContext->StyleDisplay();
>   nsIContent* const content = aItem.mContent;
>+  nsIContent* parent = content->GetParent();
>+
>+  // Push display:contents ancestors.
>+  AutoDisplayContentsAncestorPusher adcp(aState.mTreeMatchContext,
>+                                         aState.mPresContext, parent);
> 
>   // Get the parent of the content and check if it is a XBL children element.
>   // Push the children element as an ancestor here because it does
>   // not have a frame and would not otherwise be pushed as an ancestor. It is
>   // necessary to do so in order to correctly handle style resolution on
>   // descendants.
>-  nsIContent* parent = content->GetParent();
>   TreeMatchContext::AutoAncestorPusher
>     insertionPointPusher(aState.mTreeMatchContext);
>-  if (parent && nsContentUtils::IsContentInsertionPoint(parent)) {
>+  if (adcp.IsEmpty() && parent && nsContentUtils::IsContentInsertionPoint(parent)) {
>     if (aState.mTreeMatchContext.mAncestorFilter.HasFilter()) {
>       insertionPointPusher.PushAncestorAndStyleScope(parent);
>     } else {
>       insertionPointPusher.PushStyleScope(parent);
>     }
>   }
> 
>   // Push the content as a style ancestor now, so we don't have to do
>@@ -3728,16 +3708,18 @@ nsCSSFrameConstructor::ConstructFrameFro
>   if (aState.mTreeMatchContext.mAncestorFilter.HasFilter()) {
>     ancestorPusher.PushAncestorAndStyleScope(content);
>   } else {
>     ancestorPusher.PushStyleScope(content);
>   }
> 
>   nsIFrame* newFrame;
>   nsIFrame* primaryFrame;
>+  nsStyleContext* const styleContext = aItem.mStyleContext;
>+  const nsStyleDisplay* display = styleContext->StyleDisplay();
>   if (bits & FCDATA_FUNC_IS_FULL_CTOR) {
>     newFrame =
>       (this->*(data->mFullConstructor))(aState, aItem, aParentFrame,
>                                         display, aFrameItems);
>     MOZ_ASSERT(newFrame, "Full constructor failed");
>     primaryFrame = newFrame;
>   } else {
>     newFrame =
>@@ -4494,17 +4476,18 @@ nsCSSFrameConstructor::FindDisplayData(c
>                                        nsStyleContext* aStyleContext)
> {
>   PR_STATIC_ASSERT(eParentTypeCount < (1 << (32 - FCDATA_PARENT_TYPE_OFFSET)));
> 
>   // The style system ensures that floated and positioned frames are
>   // block-level.
>   NS_ASSERTION(!(aDisplay->IsFloatingStyle() ||
>                  aDisplay->IsAbsolutelyPositionedStyle()) ||
>-               aDisplay->IsBlockOutsideStyle(),
>+               aDisplay->IsBlockOutsideStyle() ||
>+               aDisplay->mDisplay == NS_STYLE_DISPLAY_CONTENTS,
>                "Style system did not apply CSS2.1 section 9.7 fixups");
> 
>   // If this is "body", try propagating its scroll style to the viewport
>   // Note that we need to do this even if the body is NOT scrollable;
>   // it might have dynamically changed from scrollable to not scrollable,
>   // and that might need to be propagated.
>   // XXXbz is this the right place to do this?  If this code moves,
>   // make this function static.
>@@ -4635,19 +4618,26 @@ nsCSSFrameConstructor::FindDisplayData(c
>                        &nsCSSFrameConstructor::ConstructTableCol) },
>     { NS_STYLE_DISPLAY_TABLE_ROW,
>       FULL_CTOR_FCDATA(FCDATA_IS_TABLE_PART |
>                        FCDATA_DESIRED_PARENT_TYPE_TO_BITS(eTypeRowGroup),
>                        &nsCSSFrameConstructor::ConstructTableRowOrRowGroup) },
>     { NS_STYLE_DISPLAY_TABLE_CELL,
>       FULL_CTOR_FCDATA(FCDATA_IS_TABLE_PART |
>                        FCDATA_DESIRED_PARENT_TYPE_TO_BITS(eTypeRow),
>-                       &nsCSSFrameConstructor::ConstructTableCell) }
>+                       &nsCSSFrameConstructor::ConstructTableCell) },
>+    { NS_STYLE_DISPLAY_CONTENTS,
>+      FULL_CTOR_FCDATA(FCDATA_IS_CONTENTS, nullptr/*never called*/) }
>   };
> 
>+  // See the mDisplay fixup code in nsRuleNode::ComputeDisplayData.
>+  MOZ_ASSERT(aDisplay->mDisplay != NS_STYLE_DISPLAY_CONTENTS ||
>+             !aElement->IsRootOfNativeAnonymousSubtree(),
>+             "display:contents on anonymous content is unsupported");
>+
>   return FindDataByInt(aDisplay->mDisplay,
>                        aElement, aStyleContext, sDisplayData,
>                        ArrayLength(sDisplayData));
> }
> 
> nsIFrame*
> nsCSSFrameConstructor::ConstructScrollableBlock(nsFrameConstructorState& aState,
>                                                 FrameConstructionItem&   aItem,
>@@ -4754,31 +4744,32 @@ nsCSSFrameConstructor::InitAndRestoreFra
>   }
> }
> 
> already_AddRefed<nsStyleContext>
> nsCSSFrameConstructor::ResolveStyleContext(nsIFrame*         aParentFrame,
>                                            nsIContent*       aContent,
>                                            nsFrameConstructorState* aState)
> {
>-  nsStyleContext* parentStyleContext = nullptr;
>-  NS_ASSERTION(aContent->GetParent(), "Must have parent here");
>-
>-  aParentFrame = nsFrame::CorrectStyleParentFrame(aParentFrame, nullptr);
>-
>-  if (aParentFrame) {
>-    // Resolve the style context based on the content object and the parent
>-    // style context
>-    parentStyleContext = aParentFrame->StyleContext();
>-  } else {
>-    // Perhaps aParentFrame is a canvasFrame and we're replicating
>-    // fixed-pos frames.
>-    // XXX should we create a way to tell ConstructFrame which style
>-    // context to use, and pass it the style context for the
>-    // previous page's fixed-pos frame?
>+  nsIContent* container = aContent->GetParent();
>+  NS_ASSERTION(container, "Must have parent here");
>+  nsStyleContext* parentStyleContext = GetDisplayContentsStyleFor(container);
>+  if (MOZ_LIKELY(!parentStyleContext)) {
>+    aParentFrame = nsFrame::CorrectStyleParentFrame(aParentFrame, nullptr);
>+    if (aParentFrame) {
>+      // Resolve the style context based on the content object and the parent
>+      // style context
>+      parentStyleContext = aParentFrame->StyleContext();
>+    } else {
>+      // Perhaps aParentFrame is a canvasFrame and we're replicating
>+      // fixed-pos frames.
>+      // XXX should we create a way to tell ConstructFrame which style
>+      // context to use, and pass it the style context for the
>+      // previous page's fixed-pos frame?
>+    }
>   }
> 
>   return ResolveStyleContext(parentStyleContext, aContent, aState);
> }
> 
> already_AddRefed<nsStyleContext>
> nsCSSFrameConstructor::ResolveStyleContext(nsStyleContext* aParentStyleContext,
>                                            nsIContent* aContent,
>@@ -5289,22 +5280,20 @@ nsCSSFrameConstructor::AddPageBreakItem(
> 
>   // Lie about the tag and namespace so we don't trigger anything
>   // interesting during frame construction.
>   aItems.AppendItem(&sPageBreakData, aContent, nsCSSAnonBoxes::pageBreak,
>                     kNameSpaceID_None, nullptr, pseudoStyle.forget(),
>                     true, nullptr);
> }
> 
>-void
>-nsCSSFrameConstructor::AddFrameConstructionItems(nsFrameConstructorState& aState,
>+bool
>+nsCSSFrameConstructor::ShouldCreateItemsForChild(nsFrameConstructorState& aState,
>                                                  nsIContent* aContent,
>-                                                 bool aSuppressWhiteSpaceOptimizations,
>-                                                 nsContainerFrame* aParentFrame,
>-                                                 FrameConstructionItemList& aItems)
>+                                                 nsContainerFrame* aParentFrame)
> {
>   aContent->UnsetFlags(NODE_DESCENDANTS_NEED_FRAMES | NODE_NEEDS_FRAME);
>   if (aContent->IsElement()) {
>     // We can't just remove our pending restyle flags, since we may
>     // have restyle-later-siblings set on us.  But we _can_ remove the
>     // "is possible restyle root" flags, and need to.  Otherwise we can
>     // end up with stale such flags (e.g. if we used to have a
>     // display:none parent when our last restyle was posted and
>@@ -5315,50 +5304,79 @@ nsCSSFrameConstructor::AddFrameConstruct
> 
>   // XXX the GetContent() != aContent check is needed due to bug 135040.
>   // Remove it once that's fixed.
>   if (aContent->GetPrimaryFrame() &&
>       aContent->GetPrimaryFrame()->GetContent() == aContent &&
>       !aState.mCreatingExtraFrames) {
>     NS_ERROR("asked to create frame construction item for a node that already "
>              "has a frame");
>-    return;
>+    return false;
>   }
> 
>   // don't create a whitespace frame if aParent doesn't want it
>   if (!NeedFrameFor(aState, aParentFrame, aContent)) {
>-    return;
>+    return false;
>   }
> 
>   // never create frames for comments or PIs
>   if (aContent->IsNodeOfType(nsINode::eCOMMENT) ||
>-      aContent->IsNodeOfType(nsINode::ePROCESSING_INSTRUCTION))
>-    return;
>-
>-  nsRefPtr<nsStyleContext> styleContext;
>-  styleContext = ResolveStyleContext(aParentFrame, aContent, &aState);
>-
>+      aContent->IsNodeOfType(nsINode::ePROCESSING_INSTRUCTION)) {
>+    return false;
>+  }
>+
>+  return true;
>+}
>+
>+void
>+nsCSSFrameConstructor::DoAddFrameConstructionItems(nsFrameConstructorState& aState,
>+                                                   nsIContent* aContent,
>+                                                   nsStyleContext* aStyleContext,
>+                                                   bool aSuppressWhiteSpaceOptimizations,
>+                                                   nsContainerFrame* aParentFrame,
>+                                                   nsTArray<nsIAnonymousContentCreator::ContentInfo>* aAnonChildren,
>+                                                   FrameConstructionItemList& aItems)
>+{
>   uint32_t flags = ITEM_ALLOW_XBL_BASE | ITEM_ALLOW_PAGE_BREAK;
>-  if (aParentFrame->IsSVGText()) {
>-    flags |= ITEM_IS_WITHIN_SVG_TEXT;
>-  }
>-  if (aParentFrame->GetType() == nsGkAtoms::blockFrame &&
>-      aParentFrame->GetParent() &&
>-      aParentFrame->GetParent()->GetType() == nsGkAtoms::svgTextFrame) {
>-    flags |= ITEM_ALLOWS_TEXT_PATH_CHILD;
>+  if (aParentFrame) {
>+    if (aParentFrame->IsSVGText()) {
>+      flags |= ITEM_IS_WITHIN_SVG_TEXT;
>+    }
>+    if (aParentFrame->GetType() == nsGkAtoms::blockFrame &&
>+        aParentFrame->GetParent() &&
>+        aParentFrame->GetParent()->GetType() == nsGkAtoms::svgTextFrame) {
>+      flags |= ITEM_ALLOWS_TEXT_PATH_CHILD;
>+    }
>   }
>   AddFrameConstructionItemsInternal(aState, aContent, aParentFrame,
>                                     aContent->Tag(), aContent->GetNameSpaceID(),
>                                     aSuppressWhiteSpaceOptimizations,
>-                                    styleContext,
>-                                    flags, nullptr,
>+                                    aStyleContext,
>+                                    flags, aAnonChildren,
>                                     aItems);
> }
> 
> void
>+nsCSSFrameConstructor::AddFrameConstructionItems(nsFrameConstructorState& aState,
>+                                                 nsIContent* aContent,
>+                                                 bool aSuppressWhiteSpaceOptimizations,
>+                                                 nsContainerFrame* aParentFrame,
>+                                                 FrameConstructionItemList& aItems)
>+{
>+  if (!ShouldCreateItemsForChild(aState, aContent, aParentFrame)) {
>+    return;
>+  }
>+  nsRefPtr<nsStyleContext> styleContext =
>+    ResolveStyleContext(aParentFrame, aContent, &aState);
>+  DoAddFrameConstructionItems(aState, aContent, styleContext,
>+                              aSuppressWhiteSpaceOptimizations, aParentFrame,
>+                              nullptr, aItems);
>+}
>+
>+void
> nsCSSFrameConstructor::SetAsUndisplayedContent(nsFrameConstructorState& aState,
>                                                FrameConstructionItemList& aList,
>                                                nsIContent* aContent,
>                                                nsStyleContext* aStyleContext,
>                                                bool aIsGeneratedContent)
> {
>   if (aStyleContext->GetPseudo()) {
>     if (aIsGeneratedContent) {
>@@ -5557,16 +5575,76 @@ nsCSSFrameConstructor::AddFrameConstruct
>     !display->IsAbsolutelyPositionedStyle() &&
>     !(bits & FCDATA_IS_TABLE_PART) &&
>     !(bits & FCDATA_IS_SVG_TEXT);
> 
>   if (canHavePageBreak && display->mBreakBefore) {
>     AddPageBreakItem(aContent, aStyleContext, aItems);
>   }
> 
>+  if (MOZ_UNLIKELY(bits & FCDATA_IS_CONTENTS)) {
>+    if (!GetDisplayContentsStyleFor(aContent)) {
>+      MOZ_ASSERT(styleContext->GetPseudo() || !isGeneratedContent,
>+                 "Should have had pseudo type");
>+      aState.mFrameManager->SetDisplayContents(aContent, styleContext);
>+    } else {
>+      aState.mFrameManager->ChangeDisplayContents(aContent, styleContext);
>+    }
>+
>+    TreeMatchContext::AutoAncestorPusher ancestorPusher(aState.mTreeMatchContext);
>+    if (aState.mTreeMatchContext.mAncestorFilter.HasFilter()) {
>+      ancestorPusher.PushAncestorAndStyleScope(aContent->AsElement());
>+    } else {
>+      ancestorPusher.PushStyleScope(aContent->AsElement());
>+    }
>+
>+    if (aParentFrame) {
>+      aParentFrame->AddStateBits(NS_FRAME_MAY_HAVE_GENERATED_CONTENT);
>+    }
>+    CreateGeneratedContentItem(aState, aParentFrame, aContent, styleContext,
>+                               nsCSSPseudoElements::ePseudo_before, aItems);
>+
>+    FlattenedChildIterator iter(aContent);
>+    for (nsIContent* child = iter.GetNextChild(); child; child = iter.GetNextChild()) {
>+      if (!ShouldCreateItemsForChild(aState, child, aParentFrame)) {
>+        continue;
>+      }
>+
>+      // Get the parent of the content and check if it is a XBL children element
>+      // (if the content is a children element then parent != aContent because the
>+      // FlattenedChildIterator will transitively iterate through <xbl:children>
>+      // for default content). Push the children element as an ancestor here because
>+      // it does not have a frame and would not otherwise be pushed as an ancestor.
>+      nsIContent* parent = child->GetParent();
>+      MOZ_ASSERT(parent, "Parent must be non-null because we are iterating children.");
>+      TreeMatchContext::AutoAncestorPusher ancestorPusher(aState.mTreeMatchContext);
>+      if (parent != aContent && parent->IsElement()) {
>+        if (aState.mTreeMatchContext.mAncestorFilter.HasFilter()) {
>+          ancestorPusher.PushAncestorAndStyleScope(parent->AsElement());
>+        } else {
>+          ancestorPusher.PushStyleScope(parent->AsElement());
>+        }
>+      }
>+
>+      nsRefPtr<nsStyleContext> childContext =
>+        ResolveStyleContext(styleContext, child, nullptr);
>+      DoAddFrameConstructionItems(aState, child, childContext,
>+                                  aSuppressWhiteSpaceOptimizations,
>+                                  aParentFrame, aAnonChildren, aItems);
>+    }
>+    aItems.SetParentHasNoXBLChildren(!iter.XBLInvolved());
>+
>+    CreateGeneratedContentItem(aState, aParentFrame, aContent, styleContext,
>+                               nsCSSPseudoElements::ePseudo_after, aItems);
>+    if (canHavePageBreak && display->mBreakAfter) {
>+      AddPageBreakItem(aContent, aStyleContext, aItems);
>+    }
>+    return;
>+  }
>+
>   FrameConstructionItem* item =
>     aItems.AppendItem(data, aContent, aTag, aNameSpaceID,
>                       pendingBinding, styleContext.forget(),
>                       aSuppressWhiteSpaceOptimizations, aAnonChildren);
>   if (!item) {
>     if (isGeneratedContent) {
>       aContent->UnbindFromTree();
>     }
>@@ -5919,31 +5997,76 @@ nsCSSFrameConstructor::GetFloatContainin
> 
> /**
>  * This function will check whether aContainer has :after generated content.
>  * If so, appending to it should actually insert.  The return value is the
>  * parent to use for newly-appended content.  *aAfterFrame points to the :after
>  * frame before which appended content should go, if there is one.
>  */
> static nsContainerFrame*
>-AdjustAppendParentForAfterContent(nsPresContext* aPresContext,
>+AdjustAppendParentForAfterContent(nsFrameManager* aFrameManager,
>                                   nsIContent* aContainer,
>                                   nsContainerFrame* aParentFrame,
>+                                  nsIContent* aChild,
>                                   nsIFrame** aAfterFrame)
> {
>-  // See if the parent has an :after pseudo-element.  Check for the presence
>-  // of style first, since nsLayoutUtils::GetAfterFrame is sorta expensive.
>-  nsStyleContext* parentStyle = aParentFrame->StyleContext();
>-  if (nsLayoutUtils::HasPseudoStyle(aContainer, parentStyle,
>+  // If the parent frame has any pseudo-elements or aContainer is a
>+  // display:contents node then we need to walk through the child
>+  // frames to find the first one that is either a ::after frame for an
>+  // ancestor of aChild or a frame that is for a node later in the
>+  // document than aChild and return that in aAfterFrame.
>+  if (GetGenConPseudos(aParentFrame) ||
>+      nsLayoutUtils::HasPseudoStyle(aContainer, aParentFrame->StyleContext(),
>                                     nsCSSPseudoElements::ePseudo_after,
>-                                    aPresContext)) {
>-    // Ensure that the :after frame is on the principal child list.
>-    aParentFrame->DrainSelfOverflowList();
>-
>-    nsIFrame* afterFrame = nsLayoutUtils::GetAfterFrame(aParentFrame);
>+                                    aParentFrame->PresContext()) ||
>+      aFrameManager->GetDisplayContentsStyleFor(aContainer)) {
>+    nsIFrame* afterFrame = nullptr;
>+    nsContainerFrame* parent =
>+      static_cast<nsContainerFrame*>(aParentFrame->LastContinuation());
>+    bool done = false;
>+    while (!done && parent) {
>+      // Ensure that all normal flow children are on the principal child list.
>+      parent->DrainSelfOverflowList();
>+
>+      nsIFrame* child = parent->GetLastChild(nsIFrame::kPrincipalList);
>+      if (child && child->IsPseudoFrame(aContainer) &&
>+          !child->IsGeneratedContentFrame()) {
>+        // Drill down into non-generated pseudo frames of aContainer.
>+        parent = nsLayoutUtils::LastContinuationWithChild(do_QueryFrame(child));
>+        continue;
>+      }
>+
>+      for (; child; child = child->GetPrevSibling()) {
>+        nsIContent* c = child->GetContent();
>+        if (child->IsGeneratedContentFrame()) {
>+          nsIContent* p = c->GetParent();
>+          if (c->Tag() == nsGkAtoms::mozgeneratedcontentafter) {
>+            if (!nsContentUtils::ContentIsDescendantOf(aChild, p) &&
>+                c->GetBindingParent() != aContainer &&
>+                nsContentUtils::PositionIsBefore(p, aChild)) {
>+              // ::after generated content for content earlier in the doc and not
>+              // for an ancestor.
>+              done = true;
>+              break;
>+            }
>+          } else if (nsContentUtils::PositionIsBefore(p, aChild)) {
>+            // Non-::after generated content for content earlier in the doc.
>+            done = true;
>+            break;
>+          }
>+        } else if (nsContentUtils::PositionIsBefore(c, aChild)) {
>+          // Content is before aChild.
>+          done = true;
>+          break;
>+        }
>+        afterFrame = child;
>+      }
>+
>+      parent = static_cast<nsContainerFrame*>(parent->GetPrevContinuation());
>+    }
>     if (afterFrame) {
>       *aAfterFrame = afterFrame;
>       return afterFrame->GetParent();
>     }
>   }
> 
>   *aAfterFrame = nullptr;
> 
>@@ -6314,17 +6437,18 @@ nsCSSFrameConstructor::GetInsertionPrevS
>   *aIsAppend = false;
> 
>   // Find the frame that precedes the insertion point. Walk backwards
>   // from the parent frame to get the parent content, because if an
>   // XBL insertion point is involved, we'll need to use _that_ to find
>   // the preceding frame.
> 
>   NS_PRECONDITION(aParentFrame, "Must have parent frame to start with");
>-  nsIContent* container = aParentFrame->GetContent();
>+  const bool boxContents = GetDisplayContentsStyleFor(aContainer);
>+  nsIContent* container = boxContents ? aContainer : aParentFrame->GetContent();
> 
>   FlattenedChildIterator iter(container);
>   bool xblCase = iter.XBLInvolved() || container != aContainer;
>   if (xblCase || !aChild->IsRootOfAnonymousSubtree()) {
>     // The check for IsRootOfAnonymousSubtree() is because editor is
>     // severely broken and calls us directly for native anonymous
>     // nodes that it creates.
>     if (aStartSkipChild) {
>@@ -6344,29 +6468,35 @@ nsCSSFrameConstructor::GetInsertionPrevS
>   uint8_t childDisplay = UNSET_DISPLAY;
>   nsIFrame* prevSibling = FindPreviousSibling(iter, childDisplay);
> 
>   // Now, find the geometric parent so that we can handle
>   // continuations properly. Use the prev sibling if we have it;
>   // otherwise use the next sibling.
>   if (prevSibling) {
>     aParentFrame = prevSibling->GetParent()->GetContentInsertionFrame();
>-  }
>-  else {
>+  } else {
>     // If there is no previous sibling, then find the frame that follows
>     if (aEndSkipChild) {
>       iter.Seek(aEndSkipChild);
>       iter.GetPreviousChild();
>     }
>     nsIFrame* nextSibling = FindNextSibling(iter, childDisplay);
>-
>+    if (boxContents) {
>+      if (nextSibling) {
>+        aParentFrame = nextSibling->GetParent()->GetContentInsertionFrame();
>+        return nextSibling->GetPrevSibling();
>+      }
>+      return GetInsertionPrevSibling(aParentFrame, aContainer->GetParent(),
>+                                     aContainer, aIsAppend,
>+                                     aIsRangeInsertSafe, nullptr, nullptr);
>+    }
>     if (nextSibling) {
>       aParentFrame = nextSibling->GetParent()->GetContentInsertionFrame();
>-    }
>-    else {
>+    } else {
>       // No previous or next sibling, so treat this like an appended frame.
>       *aIsAppend = true;
>       if (IsFramePartOfIBSplit(aParentFrame)) {
>         // Since we're appending, we'll walk to the last anonymous frame
>         // that was created for the broken inline frame.  But don't walk
>         // to the trailing inline if it's empty; stop at the block.
>         aParentFrame = GetLastIBSplitSibling(aParentFrame, false);
>       }
>@@ -6374,27 +6504,57 @@ nsCSSFrameConstructor::GetInsertionPrevS
>       // before the AdjustAppendParentForAfterContent call.
>       aParentFrame = nsLayoutUtils::LastContinuationWithChild(aParentFrame);
>       // Deal with fieldsets
>       aParentFrame = ::GetAdjustedParentFrame(aParentFrame,
>                                               aParentFrame->GetType(),
>                                               aChild);
>       nsIFrame* appendAfterFrame;
>       aParentFrame =
>-        ::AdjustAppendParentForAfterContent(mPresShell->GetPresContext(),
>-                                            container, aParentFrame,
>-                                            &appendAfterFrame);
>+        ::AdjustAppendParentForAfterContent(this, container, aParentFrame,
>+                                            aChild, &appendAfterFrame);
>       prevSibling = ::FindAppendPrevSibling(aParentFrame, appendAfterFrame);
>     }
>   }
> 
>   *aIsRangeInsertSafe = (childDisplay == UNSET_DISPLAY);
>   return prevSibling;
> }
> 
>+nsContainerFrame*
>+nsCSSFrameConstructor::GetContentInsertionFrameFor(nsIContent* aContent)
>+{
>+  // Get the primary frame associated with the content
>+  nsIFrame* frame = aContent->GetPrimaryFrame();
>+
>+  if (!frame) {
>+    if (GetDisplayContentsStyleFor(aContent)) {
>+      nsIContent* parent = aContent->GetParent();
>+      frame = parent ? GetContentInsertionFrameFor(parent) : nullptr;
>+    }
>+    if (!frame) {
>+      return nullptr;
>+    }
>+  } else {
>+    // If the content of the frame is not the desired content then this is not
>+    // really a frame for the desired content.
>+    // XXX This check is needed due to bug 135040. Remove it once that's fixed.
>+    if (frame->GetContent() != aContent) {
>+      return nullptr;
>+    }
>+  }
>+
>+  nsContainerFrame* insertionFrame = frame->GetContentInsertionFrame();
>+
>+  NS_ASSERTION(!insertionFrame || insertionFrame == frame || !frame->IsLeaf(),
>+    "The insertion frame is the primary frame or the primary frame isn't a leaf");
>+
>+  return insertionFrame;
>+}
>+
> static bool
> IsSpecialFramesetChild(nsIContent* aContent)
> {
>   // IMPORTANT: This must match the conditions in nsHTMLFramesetFrame::Init.
>   return aContent->IsHTML() &&
>     (aContent->Tag() == nsGkAtoms::frameset ||
>      aContent->Tag() == nsGkAtoms::frame);
> }
>@@ -6522,16 +6682,20 @@ nsCSSFrameConstructor::MaybeConstructLaz
>     }
>     if (!noPrimaryFrame && !content->GetPrimaryFrame()) {
>       noPrimaryFrame = true;
>     }
>     if (!needsFrameBitSet && content->HasFlag(NODE_NEEDS_FRAME)) {
>       needsFrameBitSet = true;
>     }
> #endif
>+    // XXXmats no lazy frames for display:contents descendants yet (bug 979782).
>+    if (GetDisplayContentsStyleFor(content)) {
>+      return false;
>+    }
>     content->SetFlags(NODE_DESCENDANTS_NEED_FRAMES);
>     content = content->GetFlattenedTreeParent();
>   }
> #ifdef DEBUG
>   if (content && content->GetPrimaryFrame() &&
>       content->GetPrimaryFrame()->IsLeaf()) {
>     noPrimaryFrame = needsFrameBitSet = false;
>   }
>@@ -6644,18 +6808,18 @@ void
> nsCSSFrameConstructor::IssueSingleInsertNofications(nsIContent* aContainer,
>                                                     nsIContent* aStartChild,
>                                                     nsIContent* aEndChild,
>                                                     bool aAllowLazyConstruction)
> {
>   for (nsIContent* child = aStartChild;
>        child != aEndChild;
>        child = child->GetNextSibling()) {
>-    if ((child->GetPrimaryFrame() ||
>-         GetUndisplayedContent(child))
>+    if ((child->GetPrimaryFrame() || GetUndisplayedContent(child) ||
>+         GetDisplayContentsStyleFor(child))
> #ifdef MOZ_XUL
>         //  Except listboxes suck, so do NOT skip anything here if
>         //  we plan to notify a listbox.
>         && !MaybeGetListBoxBodyFrame(aContainer, child)
> #endif
>         ) {
>       // Already have a frame or undisplayed entry for this content; a
>       // previous ContentInserted in this loop must have reconstructed
>@@ -6807,17 +6971,17 @@ nsCSSFrameConstructor::ContentAppended(n
>     nsIContent* bindingParent = aContainer->GetBindingParent();
>     LAYOUT_PHASE_TEMP_EXIT();
>     nsresult rv = RecreateFramesForContent(bindingParent, false);
>     LAYOUT_PHASE_TEMP_REENTER();
>     return rv;
>   }
> 
>   // Get the frame associated with the content
>-  nsContainerFrame* parentFrame = ::GetContentInsertionFrameFor(aContainer);
>+  nsContainerFrame* parentFrame = GetContentInsertionFrameFor(aContainer);
> 
>   // See comment in ContentRangeInserted for why this is necessary.
>   if (!parentFrame && !aContainer->IsActiveChildrenElement()) {
>     return NS_OK;
>   }
> 
>   if (aAllowLazyConstruction &&
>       MaybeConstructLazily(CONTENTAPPEND, aContainer, aFirstNewContent)) {
>@@ -6880,19 +7044,18 @@ nsCSSFrameConstructor::ContentAppended(n
>   // We should never get here with fieldsets, since they have multiple
>   // insertion points.
>   NS_ASSERTION(parentFrame->GetType() != nsGkAtoms::fieldSetFrame,
>                "Unexpected parent");
> 
>   // Deal with possible :after generated content on the parent
>   nsIFrame* parentAfterFrame;
>   parentFrame =
>-    ::AdjustAppendParentForAfterContent(mPresShell->GetPresContext(),
>-                                        aContainer, parentFrame,
>-                                        &parentAfterFrame);
>+    ::AdjustAppendParentForAfterContent(this, aContainer, parentFrame,
>+                                        aFirstNewContent, &parentAfterFrame);
> 
>   // Create some new frames
>   nsFrameConstructorState state(mPresShell,
>                                 GetAbsoluteContainingBlock(parentFrame, FIXED_POS),
>                                 GetAbsoluteContainingBlock(parentFrame, ABS_POS),
>                                 GetFloatContainingBlock(parentFrame));
>   state.mTreeMatchContext.InitAncestors(aContainer->AsElement());
> 
>@@ -7244,26 +7407,27 @@ nsCSSFrameConstructor::ContentRangeInser
>     //XXXsmaug This is super unefficient!
>     nsIContent* bindingParent = aContainer->GetBindingParent();
>     LAYOUT_PHASE_TEMP_EXIT();
>     nsresult rv = RecreateFramesForContent(bindingParent, false);
>     LAYOUT_PHASE_TEMP_REENTER();
>     return rv;
>   }
> 
>-  nsContainerFrame* parentFrame = ::GetContentInsertionFrameFor(aContainer);
>+  nsContainerFrame* parentFrame = GetContentInsertionFrameFor(aContainer);
>   // The xbl:children element won't have a frame, but default content can have the children as
>   // a parent. While its uncommon to change the structure of the default content itself, a label,
>   // for example, can be reframed by having its value attribute set or removed.
>   if (!parentFrame && !aContainer->IsActiveChildrenElement()) {
>     return NS_OK;
>   }
> 
>   // Otherwise, we've got parent content. Find its frame.
>-  NS_ASSERTION(!parentFrame || parentFrame->GetContent() == aContainer, "New XBL code is possibly wrong!");
>+  NS_ASSERTION(!parentFrame || parentFrame->GetContent() == aContainer ||
>+               GetDisplayContentsStyleFor(aContainer), "New XBL code is possibly wrong!");
> 
>   if (aAllowLazyConstruction &&
>       MaybeConstructLazily(CONTENTINSERT, aContainer, aStartChild)) {
>     return NS_OK;
>   }
> 
>   if (isSingleInsert) {
>     // See if we have an XBL insertion point. If so, then that's our
>@@ -7540,20 +7704,19 @@ nsCSSFrameConstructor::ContentRangeInser
>                  frame1->GetType() == nsGkAtoms::fieldSetFrame ||
>                  (frame1->GetParent() &&
>                   frame1->GetParent()->GetType() == nsGkAtoms::fieldSetFrame),
>                  "Unexpected frame types");
> #endif
>     isAppend = true;
>     nsIFrame* appendAfterFrame;
>     parentFrame =
>-      ::AdjustAppendParentForAfterContent(mPresShell->GetPresContext(),
>-                                          container,
>+      ::AdjustAppendParentForAfterContent(this, container,
>                                           frameItems.FirstChild()->GetParent(),
>-                                          &appendAfterFrame);
>+                                          aStartChild, &appendAfterFrame);
>     prevSibling = ::FindAppendPrevSibling(parentFrame, appendAfterFrame);
>   }
> 
>   if (haveFirstLineStyle && parentFrame == containingBlock) {
>     // It's possible that the new frame goes into a first-line
>     // frame. Look at it and see...
>     if (isAppend) {
>       // Use append logic when appending
>@@ -7683,28 +7846,42 @@ nsCSSFrameConstructor::ContentRemoved(ns
>            static_cast<void*>(aChild),
>            static_cast<void*>(aOldNextSibling));
>     if (gReallyNoisyContentUpdates) {
>       aContainer->List(stdout, 0);
>     }
>   }
> #endif
> 
>-  nsPresContext *presContext = mPresShell->GetPresContext();
>-  nsresult                  rv = NS_OK;
>-
>-  // Find the child frame that maps the content
>+  nsresult rv = NS_OK;
>   nsIFrame* childFrame = aChild->GetPrimaryFrame();
>-
>   if (!childFrame || childFrame->GetContent() != aChild) {
>     // XXXbz the GetContent() != aChild check is needed due to bug 135040.
>     // Remove it once that's fixed.
>     ClearUndisplayedContentIn(aChild, aContainer);
>   }
>-
>+  MOZ_ASSERT(!childFrame || !GetDisplayContentsStyleFor(aChild),
>+             "display:contents nodes shouldn't have a frame");
>+  if (!childFrame && GetDisplayContentsStyleFor(aChild)) {
>+    FlattenedChildIterator iter(aChild);
>+    for (nsIContent* c = iter.GetNextChild(); c; c = iter.GetNextChild()) {
>+      if (c->GetPrimaryFrame() || GetDisplayContentsStyleFor(c)) {
>+        LAYOUT_PHASE_TEMP_EXIT();
>+        rv = ContentRemoved(aChild, c, nullptr, aFlags, aDidReconstruct);
>+        LAYOUT_PHASE_TEMP_REENTER();
>+        NS_ENSURE_SUCCESS(rv, rv);
>+        if (*aDidReconstruct) {
>+          return rv;
>+        }
>+      }
>+    }
>+    ClearDisplayContentsIn(aChild, aContainer);
>+  }
>+
>+  nsPresContext* presContext = mPresShell->GetPresContext();
> #ifdef MOZ_XUL
>   if (NotifyListBoxBody(presContext, aContainer, aChild, aOldNextSibling,
>                         mDocument, childFrame, CONTENT_REMOVED))
>     return NS_OK;
> 
> #endif // MOZ_XUL
> 
>   // If we're removing the root, then make sure to remove things starting at
>@@ -8540,25 +8717,25 @@ nsCSSFrameConstructor::GetInsertionPoint
> 
>   nsIContent* insertionElement;
>   if (aChildContent) {
>     // We've got an explicit insertion child. Check to see if it's
>     // anonymous.
>     if (aChildContent->GetBindingParent() == aContainer) {
>       // This child content is anonymous. Don't use the insertion
>       // point, since that's only for the explicit kids.
>-      return ::GetContentInsertionFrameFor(aContainer);
>+      return GetContentInsertionFrameFor(aContainer);
>     }
> 
>     if (nsContentUtils::HasDistributedChildren(aContainer)) {
>       // The container distributes nodes, use the frame of the flattened tree parent.
>       // It may be the case that the node is distributed but not matched to any
>       // insertion points, so there is no flattened parent.
>       nsIContent* flattenedParent = aChildContent->GetFlattenedTreeParent();
>-      return flattenedParent ? ::GetContentInsertionFrameFor(flattenedParent) : nullptr;
>+      return flattenedParent ? GetContentInsertionFrameFor(flattenedParent) : nullptr;
>     }
> 
>     insertionElement = bindingManager->FindNestedInsertionPoint(aContainer, aChildContent);
>   }
>   else {
>     if (nsContentUtils::HasDistributedChildren(aContainer)) {
>       // The container distributes nodes to shadow DOM insertion points.
>       // Return with aMultiple set to true to induce callers to insert children
>@@ -8577,18 +8754,17 @@ nsCSSFrameConstructor::GetInsertionPoint
>       return nullptr;
>     }
>   }
> 
>   if (!insertionElement) {
>     insertionElement = aContainer;
>   }
> 
>-  nsContainerFrame* insertionPoint =
>-    ::GetContentInsertionFrameFor(insertionElement);
>+  nsContainerFrame* insertionPoint = GetContentInsertionFrameFor(insertionElement);
> 
>   // fieldsets have multiple insertion points.  Note that we might
>   // have to look at insertionElement here...
>   if (aMultiple && insertionElement->IsHTML(nsGkAtoms::fieldset)) {
>     *aMultiple = true;
>   }
> 
>   return insertionPoint;
>diff --git a/layout/base/nsCSSFrameConstructor.h b/layout/base/nsCSSFrameConstructor.h
>--- a/layout/base/nsCSSFrameConstructor.h
>+++ b/layout/base/nsCSSFrameConstructor.h
>@@ -296,16 +296,33 @@ private:
>   // may suppress the construction of white-space-only text frames
>   // must be skipped for these items and items around them.
>   void AddFrameConstructionItems(nsFrameConstructorState& aState,
>                                  nsIContent*              aContent,
>                                  bool                     aSuppressWhiteSpaceOptimizations,
>                                  nsContainerFrame*        aParentFrame,
>                                  FrameConstructionItemList& aItems);
> 
>+  // Helper method for AddFrameConstructionItems etc.
>+  // Unsets the need-frame/restyle bits on aContent.
>+  // return true iff we should attempt to create frames for aContent.
>+  bool ShouldCreateItemsForChild(nsFrameConstructorState& aState,
>+                                 nsIContent* aContent,
>+                                 nsContainerFrame* aParentFrame);
>+
>+  // Helper method for AddFrameConstructionItems etc.
>+  // Make sure ShouldCreateItemsForChild() returned true before calling this.
>+  void DoAddFrameConstructionItems(nsFrameConstructorState& aState,
>+                                   nsIContent* aContent,
>+                                   nsStyleContext* aStyleContext,
>+                                   bool aSuppressWhiteSpaceOptimizations,
>+                                   nsContainerFrame* aParentFrame,
>+                                   nsTArray<nsIAnonymousContentCreator::ContentInfo>* aAnonChildren,
>+                                   FrameConstructionItemList& aItems);
>+
>   // Construct the frames for the document element.  This can return null if the
>   // document element is display:none, or if the document element has a
>   // not-yet-loaded XBL binding, or if it's an SVG element that's not <svg>.
>   nsIFrame* ConstructDocElementFrame(Element*                 aDocElement,
>                                      nsILayoutHistoryState*   aFrameState);
> 
>   // Set up our mDocElementContainingBlock correctly for the given root
>   // content.
>@@ -587,16 +604,20 @@ private:
>   /* If FCDATA_CREATE_BLOCK_WRAPPER_FOR_ALL_KIDS is set, then create a
>      block formatting context wrapper around the kids of this frame
>      using the FrameConstructionData's mPseudoAtom for its anonymous
>      box type. */
> #define FCDATA_CREATE_BLOCK_WRAPPER_FOR_ALL_KIDS 0x40000
>   /* If FCDATA_IS_SVG_TEXT is set, then this text frame is a descendant of
>      an SVG text frame. */
> #define FCDATA_IS_SVG_TEXT 0x80000
>+  /**
>+   * display:contents
>+   */
>+#define FCDATA_IS_CONTENTS 0x100000
> 
>   /* Structure representing information about how a frame should be
>      constructed.  */
>   struct FrameConstructionData {
>     // Flag bits that can modify the way the construction happens
>     uint32_t mBits;
>     // We have exactly one of three types of functions, so use a union for
>     // better cache locality for the ones that aren't pointer-to-member.  That
>@@ -1757,16 +1778,22 @@ private:
>   nsIFrame* GetInsertionPrevSibling(nsContainerFrame*& aParentFrame, /* inout */
>                                     nsIContent* aContainer,
>                                     nsIContent* aChild,
>                                     bool* aIsAppend,
>                                     bool* aIsRangeInsertSafe,
>                                     nsIContent* aStartSkipChild = nullptr,
>                                     nsIContent *aEndSkipChild = nullptr);
> 
>+  /**
>+   * Return the insertion frame of the primary frame of aContent, or its nearest
>+   * ancestor that isn't display:contents.
>+   */
>+  nsContainerFrame* GetContentInsertionFrameFor(nsIContent* aContent);
>+
>   // see if aContent and aSibling are legitimate siblings due to restrictions
>   // imposed by table columns
>   // XXXbz this code is generally wrong, since the frame for aContent
>   // may be constructed based on tag, not based on aDisplay!
>   bool IsValidSibling(nsIFrame*              aSibling,
>                         nsIContent*            aContent,
>                         uint8_t&               aDisplay);
>

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