Adds Media.Audio.InputDevicePropertyChangedMac UMA stat on Mac

media/audio/mac/audio_low_latency_input_mac.h

Index: media/audio/mac/audio_low_latency_input_mac.h
diff --git a/media/audio/mac/audio_low_latency_input_mac.h b/media/audio/mac/audio_low_latency_input_mac.h
index 6d2d8f5e5830fa4ac344a4807df6750de8959ae3..7861186224870d05516c23dc5f487baca1e802a5 100644
--- a/media/audio/mac/audio_low_latency_input_mac.h
+++ b/media/audio/mac/audio_low_latency_input_mac.h
@@ -38,6 +38,7 @@
 
 #include <AudioUnit/AudioUnit.h>
 #include <CoreAudio/CoreAudio.h>
+#include <map>
 #include <stddef.h>
 #include <stdint.h>
 
@@ -94,6 +95,8 @@ class MEDIA_EXPORT AUAudioInputStream
   size_t requested_buffer_size() const { return number_of_frames_; }
 
  private:
+  static const AudioObjectPropertyAddress kDeviceChangePropertyAddress;
+
   // Callback functions called on a real-time priority I/O thread from the audio
   // unit. These methods are called when recorded audio is available.
   static OSStatus DataIsAvailable(void* context,
@@ -111,6 +114,23 @@ class MEDIA_EXPORT AUAudioInputStream
   OSStatus Provide(UInt32 number_of_frames, AudioBufferList* io_data,
                    const AudioTimeStamp* time_stamp);
 
+  // Callback functions called on different system threads from the Core Audio
+  // framework. These methods are called when device properties are changed.
+  static OSStatus OnDevicePropertyChanged(
+      AudioObjectID object_id,
+      UInt32 num_addresses,
+      const AudioObjectPropertyAddress addresses[],
+      void* context);
+  OSStatus DevicePropertyChanged(AudioObjectID object_id,
+                                 UInt32 num_addresses,
+                                 const AudioObjectPropertyAddress addresses[]);
+
+  // Registers OnDevicePropertyChanged() to receive notifications when device
+  // properties changes.
+  void RegisterDeviceChangeListener();
+  // Stop listening for changes in device properties.
+  void DeRegisterDeviceChangeListener();
+
   // Gets the fixed capture hardware latency and store it during initialization.
   // Returns 0 if not available.
   double GetHardwareLatency();
@@ -132,6 +152,10 @@ class MEDIA_EXPORT AUAudioInputStream
   void SetInputCallbackIsActive(bool active);
   bool GetInputCallbackIsActive();
 
+  // Helper methods to set and get atomic |device_listener_is_active_|.
+  void SetDeviceListenerIsActive(bool active);
+  bool GetDeviceListenerIsActive();
+
   // Checks if a stream was started successfully and the audio unit also starts
   // to call InputProc() as it should. This method is called once when a timer
   // expires 5 seconds after calling Start().
@@ -143,6 +167,9 @@ class MEDIA_EXPORT AUAudioInputStream
   // Adds extra UMA stats when it has been detected that startup failed.
   void AddHistogramsForFailedStartup();
 
+  // TODO(henrika): add comments
+  void AddDevicePropertyChangesToUMA();
+
   // Verifies that Open(), Start(), Stop() and Close() are all called on the
   // creating thread which is the main browser thread (CrBrowserMain) on Mac.
   base::ThreadChecker thread_checker_;
@@ -218,6 +245,11 @@ class MEDIA_EXPORT AUAudioInputStream
   // Set to true once when AudioUnitRender() succeeds for the first time.
   bool audio_unit_render_has_worked_;
 
+  std::map<UInt32, int> device_property_changes_map_;
+
+  // Set to true when we are listening for changes in device properties.
+  base::subtle::Atomic32 device_listener_is_active_;
+
   DISALLOW_COPY_AND_ASSIGN(AUAudioInputStream);
 };