Milestone for this feature is defined as:
- The feature should be disabled by default behind a pref
- It should be possible for a user to somehow invoke Picture in Picture on a video element
- The opened window should be an "always on top" window, at least on Windows.
- Only one Picture in Picture window should be openable at a time.
- The video playing in the "always on top" window should not incur a new network request to the service hosting the video.
- The video playing in the "always on top" window should begin automatically.
This first milestone will be pretty rough, and essentially consists of cleaning up some demonstration patches that were written so that UX can try the feature and figure out how best to steer it.