In streaming mode it is preferable to fade to silence when sender stops sending, or long period of packet loss.
In streaming mode it is preferable to fade to silence when sender stops sending, or long period of packet loss.

test=try bots.
Review URL: https://webrtc-codereview.appspot.com/1272004

git-svn-id: 03ae4fbe531b1eefc9d815f31e49022782c42458@3771 4adac7df-926f-26a2-2b94-8c16560cd09d

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