gyzhou f6bcac59e8 Support external audio mixer in webrtc.
An external audio mixer will be passed from PeerConnectionFactory to
AudioTransportProxy.

BUG=webrtc:6457

Review-Url: https://codereview.webrtc.org/2539213003
Cr-Commit-Position: refs/heads/master@{#15556}
2016-12-13 00:25:16 +00:00
..
2016-09-29 00:42:08 +00:00