This is a tracking issue for the work remaining to migrate our Chrome Extensions support away from our ad-hoc polyfills to the official //extensions code in Chromium.

• Preliminary support behind a feature flag feat: preliminary support for //extensions #17440
• Sketch out complete API
  • Should include:
    • Loading and unloading extensions
    • Callbacks for relevant events
    • Exposing relevant info, e.g. badging, notifications, other requests from extensions that the main process might want or need to intervene in
• Load extensions on the IO thread instead of the main thread
• Support for background pages feat: [extensions] background pages #21591
• Support for devtools extensions feat: just enough //extensions to load a simple devtools extension #19515 feat: [extensions] implement a couple of tabs APIs #21779
• API Documentation docs: document new extensions APIs #21809
• Deprecate polyfill-based extensions support chore: [extensions] support old APIs with enable_electron_extensions #21812
• Enable feature flag by default feat: enable native extensions support #21814
• Remove old extensions code refactor: remove JS for non-native extensions shim #23340
• Finalize API
• Assess all TODOs