Mute audio when volume is zero on Android.

media/audio/android/opensles_output.h

Index: media/audio/android/opensles_output.h
diff --git a/media/audio/android/opensles_output.h b/media/audio/android/opensles_output.h
index 7232d5da5f76210dee252f44946d141d075e19be..623b0193894ba87633dd3ec009565dfc094546ed 100644
--- a/media/audio/android/opensles_output.h
+++ b/media/audio/android/opensles_output.h
@@ -40,6 +40,10 @@ class OpenSLESOutputStream : public AudioOutputStream {
   virtual void SetVolume(double volume) OVERRIDE;
   virtual void GetVolume(double* volume) OVERRIDE;
 
+  // Set the value of |muted_|. It does not affect |volume_| which can be
+  // got by calling GetVolume(). See comments for |muted_| below.
+  void SetMute(bool muted);
+
  private:
   bool CreatePlayer();
 
@@ -96,6 +100,12 @@ class OpenSLESOutputStream : public AudioOutputStream {
 
   bool started_;
 
+  // Volume control coming from hardware. It overrides |volume_| when it's
+  // true. Otherwise, use |volume_| for scaling.
+  // This is needed because platform voice volume never goes to zero in
+  // COMMUNICATION mode on Android.
+  bool muted_;
+
   // Volume level from 0 to 1.
   float volume_;