Add AudioSendStream::SetMuted() method and use it in WVoMC::MuteStream().

webrtc/media/engine/fakewebrtccall.h

Index: webrtc/media/engine/fakewebrtccall.h
diff --git a/webrtc/media/engine/fakewebrtccall.h b/webrtc/media/engine/fakewebrtccall.h
index 8ca45f72d3228e77ef742696320b6d75bb054ce3..8682805b3fb68a4acf78cb8f6181e55f9935d6c4 100644
--- a/webrtc/media/engine/fakewebrtccall.h
+++ b/webrtc/media/engine/fakewebrtccall.h
@@ -46,6 +46,7 @@ class FakeAudioSendStream final : public webrtc::AudioSendStream {
   void SetStats(const webrtc::AudioSendStream::Stats& stats);
   TelephoneEvent GetLatestTelephoneEvent() const;
   bool IsSending() const { return sending_; }
+  bool muted() const { return muted_; }
 
  private:
   // webrtc::AudioSendStream implementation.
@@ -54,12 +55,14 @@ class FakeAudioSendStream final : public webrtc::AudioSendStream {
 
   bool SendTelephoneEvent(int payload_type, int event,
                           int duration_ms) override;
+  void SetMuted(bool muted) override;
   webrtc::AudioSendStream::Stats GetStats() const override;
 
   TelephoneEvent latest_telephone_event_;
   webrtc::AudioSendStream::Config config_;
   webrtc::AudioSendStream::Stats stats_;
   bool sending_ = false;
+  bool muted_ = false;
 };
 
 class FakeAudioReceiveStream final : public webrtc::AudioReceiveStream {