GitLab

There are 3 big changes;
1. Initialize and bind StreamTextureProxy to the impl thread when the main
thread is blocked.
2. Set stream texture size when the video size is changed, instead of adhoc in
rendering code.
3. Add lots of thread checks.

BUG=N/A

Review URL: https://codereview.chromium.org/448063003

Cr-Commit-Position: refs/heads/master@{#289315}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@289315 0039d316-1c4b-4281-b951-d872f2087c98