When producing extension specs, it is a bit difficult to specify where new steps should be slotted in wrt to the getDisplayMedia() algorithm.

I propose that where we currently have the following step:

9. Resolve p with stream and abort these steps.

We could have a preceding step:

9. Run <dfn class="export">getDisplayMedia pre-resolution extension steps</dfn>.
10. Resolve p with stream and abort these steps.

There could be a note explaining how these extension steps are defined in other specs and must be agnostic of the order in which they are executed.