Deprecate WebKitMediaSource implementation to encourage migration to unprefixed MediaSource implementation.
The unprefixed MediaSource implementation contains all of the functionality of the prefixed API and the Media Source Extension spec has reached CR so web developers should be using what has actually been standardized.
I haven't add a counter yet, but plan to add one and a deprecation warning today. The unprefixed MediaSource API has been available since M31 so any apps still using the prefixed API should be able to update their code and playback on stable channel Chome builds should still work.
The prefixed API and unprefixed API have slightly different method signatures and event names, but equivalent functionality and events are available in the unprefixed API. The main difference between the 2 APIs is that appending media data is a synchronous operation in the prefixed API and it is asynchronous in the unprefixed API. Web developers will have to update their code to deal with the asynchrony, but this is a pretty straightforward transformation.
Row on feature dashboard?
Requesting approval to remove too?
No. Not until we've collected use counter data and verify that early Media Source adopters like YouTube and Netflix have completely migrated over to the unprefixed API.