Add default implementation to VideoSourceInterface of Stop and Restart. This is to make sure Chrome does not break when rolling. This should be reverted once Chrome has been updated.
Add default implementation to VideoSourceInterface of Stop and Restart.
This is to make sure Chrome does not break when rolling. This should be reverted once
Chrome has been updated.

Please see:
http://build.chromium.org/p/chromium.webrtc.fyi/builders/Mac/builds/16556/steps/compile/logs/stdio

BUG=4303
R=magjed@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/35229004

Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#8391}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 1a38a511196c0aba224467d9714d9b4504cc0538

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