Add support for audio input mute detection on all platforms

media/audio/pulse/pulse_input.h

Index: media/audio/pulse/pulse_input.h
diff --git a/media/audio/pulse/pulse_input.h b/media/audio/pulse/pulse_input.h
index 60acf2f908719891974eee38326fe528b64d615d..564bfe796093888098e1affe5693f62e33dec8de 100644
--- a/media/audio/pulse/pulse_input.h
+++ b/media/audio/pulse/pulse_input.h
@@ -41,6 +41,7 @@ class PulseAudioInputStream : public AgcAudioStream<AudioInputStream> {
   virtual double GetMaxVolume() override;
   virtual void SetVolume(double volume) override;
   virtual double GetVolume() override;
+  virtual bool IsMuted() override;
 
  private:
   // PulseAudio Callbacks.
@@ -48,6 +49,8 @@ class PulseAudioInputStream : public AgcAudioStream<AudioInputStream> {
   static void StreamNotifyCallback(pa_stream* stream, void* user_data);
   static void VolumeCallback(pa_context* context, const pa_source_info* info,
                              int error, void* user_data);
+  static void MuteCallback(pa_context* context, const pa_source_info* info,
+                             int error, void* user_data);
 
   // Helper for the ReadCallback.
   void ReadData();
@@ -60,6 +63,10 @@ class PulseAudioInputStream : public AgcAudioStream<AudioInputStream> {
   double volume_;
   bool stream_started_;
 
+  // Set to true in IsMuted() if user has muted the selected microphone in the
+  // sound settings UI.
+  bool muted_;
+
   // Holds the data from the OS.
   AudioBlockFifo fifo_;