Add AudioReceiveStream::SetGain() method and use that in WVoMC::SetOutputVolume().

Removes the need to use VoEVolume::SetChannelOutputVolumeScaling().

BUG=webrtc:4690

Review-Url: https://codereview.webrtc.org/2062193002
Cr-Original-Commit-Position: refs/heads/master@{#13194}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 217fb66e16627be23b8769edded8a23f6406ddab
12 files changed