Implement SetSendCodecs() unit tests for WebRtcVideoChannel2.
Implement SetSendCodecs() unit tests for WebRtcVideoChannel2.

BUG=
R=pbos@webrtc.org, wu@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/12829004

Patch from Changbin Shao <changbin.shao@intel.com>.

Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 269605ce450545c565a77719e0167024a7d3643c

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