Removed VideoSource dependency to ChannelManager.
Instead VideoSource directly access the cricket::VideoCapturer via the worker_thread.

Document: https://docs.google.com/a/google.com/document/d/1mEIw_0uDzyHjL3l8a82WKp6AvgR8Tlwn9JGvhbUjVpY/edit?usp=sharing

BUG=webrtc:5426
R=nisse@webrtc.org, pthatcher@webrtc.org

Review URL: https://codereview.webrtc.org/1759473003 .

Cr-Original-Commit-Position: refs/heads/master@{#11852}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 0f13ec1265250a87a5390c9a0403943bcf1bbf33
6 files changed