Add support for Document Picture-in-Picture API (M111+)

[magreenblatt]

Original report by me.

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Chrome is testing a new PiP mode that supports arbitrary HTML (blog post). This works in current Chrome Dev channel (111.0.5563.19) but not in CEF M111. Demo is https://document-picture-in-picture-api.glitch.me/

With Alloy runtime, this fails with ReferenceError: documentPictureInPicture is not defined.

With Chome runtime, this creates a fully styled popup window (vs expected window with minimal frame).

With Chrome Dev channel (expected result):

‌

[magreenblatt]

chrome: Use default Browser creation for picture-in-picture popups (see issue #3448)

→ <<cset 82dc13a87001 (bb)>>

[magreenblatt]

This now works as expected with the Chrome runtime in 5563 release branch but not current master (based on M111), due to additional Chromium fixes that have been cherry-picked to the release branch.

[magreenblatt]

chrome: Use default Browser creation for picture-in-picture popups (see issue #3448)

Note: In current master (based on M111), document PiP partially works when
run with the --enable-features=DocumentPictureInPictureAPI command-line
flag. However, the document PiP implementation at this Chromium version is
missing fixes that have already been cherry-picked to the 5563 release
branch. Those fixes will only be available in master after the next Chromium
update (to M112).

→ <<cset ff68c0154323 (bb)>>

[magreenblatt]

The Chrome runtime is now supported. The Alloy runtime will not be supported at this time.

[magreenblatt]

• changed state from "new" to "resolved"