Make sure webrtc::VideoSourceInterface is released on the main render thread.
webrtc::VideoSourceInterface must be released on the main render thread since it needs a libjingle thread wrapper. Fix problem with where a const scoped_refptr<webrtc::VideoSourceInterface>& source must be released on the main render thread. The problem was introduced in https://codereview.chromium.org/
252393006/ where the video frames are now delivered on the IO-thread that may result in that that WebRtcVideoTrackAdapter::WebRtcVideoSourceAdapter that holds the last reference to it is destroyed on the IO-thread.
TEST= http://googlechrome.github.io/webrtc/samples/web/content/constraints/ click Ge media and click Connect. When video is flowing, refresh the page.
R=tommi@chromium.org
Review URL: https://codereview.chromium.org/
279533003
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@269222 0039d316-1c4b-4281-b951-d872f2087c98