Implement disabling and enabling media tracks
This CL implements disabling and enabling audio and video streams via
Javascript media tracks API. When a media track is disabled, the
corresponding DemuxerStream generates an EOS notification, thus ending
further decoding/rendering of that stream. When a media track is
enabled, the corresponding DemuxerStream is seeked to the current
playback position and we notify the renderers to resume reading from
the demuxer stream and rendering its contents.
BUG=249427
Review-Url: https://codereview.chromium.org/1935873002
Cr-Commit-Position: refs/heads/master@{#403403}
32 files changed
