GitLab

Makes sure that all interaction with the video decoder is done on the VIDEO_DECODER thread.
Logging which was removed here, will be added in a follow  up cl.

Review URL: https://codereview.chromium.org/80383006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238535 0039d316-1c4b-4281-b951-d872f2087c98