Move VoiceEngineObserver into AudioSendStream so that we detect typing noises and return properly in GetStats().

BUG=webrtc:4690

Review URL: https://codereview.webrtc.org/1403363003

Cr-Original-Commit-Position: refs/heads/master@{#10548}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 566ef247b9779f6c9d0e7ec9eea6b037f4682c53
20 files changed