Revert "Add default implementation to VideoSourceInterface."
Chrome test mock has been updated so VideoSourceInterface can now be pure virtual again. This reverts commit ed8d52378c43a7a93e0d2ca586486ca06db9eabe.

R=magjed@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/45399004

Cr-Commit-Position: refs/heads/master@{#8551}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8551 4adac7df-926f-26a2-2b94-8c16560cd09d
1 file changed