Implements MediaStreamVideoSource.

1) Add MediaStreamDependencyFactory::CreateVideoSource to create a webrtc::VideoSourceInterface that's associated with given capturer.
2) Implement MediaStreamVideoSource:
  * Creates a webrtc::VideoSource instance with a fake cricket::VideoCapturer. Use this webrtc::VideoSource as the adapter to talk to the libjingle world.
  * When AddTrack is called, creates native track for the given blink track. And connect the native track with the webrtc::VideoSource so that the track can get frames from this source.
  * When DeliverVideoFrame is called, feeds the frame to all the registered tracks via the adapter (webrtc::VideoSource)'s FrameInput interface.


BUG=334241
R=joi@chromium.org, perkj@chromium.org, xians@chromium.org

Review URL: https://codereview.chromium.org/129923002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245001 0039d316-1c4b-4281-b951-d872f2087c98
Suppress a w3c test for Shadow DOM.

This is a pre-requirement patch to land https://codereview.chromium.org/137993003/.

I am going to follow the following procedure:

1. Suppress a w3c test which would fail if I land https://codereview.chromium.org/137993003/
2. Land https://codereview.chromium.org/137993003/
3. Update the w3c test and upstream it to the w3c repository
4. Wait until the test is imported to blink.
5. Remove the suppression.

BUG=334152

Review URL: https://codereview.chromium.org/138143005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245002 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245002