RELAND: Merge VideoSenderConfig and AudioSenderConfig.

This is a re-land of https://codereview.chromium.org/2113783002/ with
fix on cast_h264_vt_encoder_unittests.

-------Description of original change follows-------

Refactoring: Merge VideoSenderConfig and AudioSenderConfig.
In the CL: 1) VideoSenderConfig and AudioSenderConfig are merged to
FrameSenderConfig. 2) CastRtpParams is removed . RtpParams is directly
converted to/from FrameSenderConfig.

BUG=530839

Review-Url: https://codereview.chromium.org/2133903002
Cr-Commit-Position: refs/heads/master@{#404975}
49 files changed