stack will be removed soon in a separate CL. Constraints will not be supported
in the new implementation. Apps can request a format directly and the closest
supported format will be selected.
Changes needed from the apps:
1. Use the new createVideoSource without constraints.
2. Call startCapture manually.
3. Don't call videoSource.stop/restart, use startCapture/stopCapture instead.
R=magjed@webrtc.orgTBR=kjellander@webrtc.org
Review URL: https://codereview.webrtc.org/2127893002 .
Cr-Commit-Position: refs/heads/master@{#13504}
