This CL makes sure the real VideoTrackSourceInterface implementation is destroyed on the signaling thread and marshals all method calls to the signaling thread. This is done using VideoTrackSourceProxy. Bug: webrtc:7767 Change-Id: Iba3b67bb32a684ba289bc8b9981585ea58084359 Reviewed-on: https://chromium-review.googlesource.com/526634 Commit-Queue: Magnus Jedvert <magjed@webrtc.org> Reviewed-by: Niels Moller <nisse@webrtc.org> Cr-Commit-Position: refs/heads/master@{#18476}