Improve logging related to start/stop and failure of audio input streams in Chrome

media/audio/audio_manager.h

Index: media/audio/audio_manager.h
diff --git a/media/audio/audio_manager.h b/media/audio/audio_manager.h
index 915308ef77d89cfea1470ee0b1696d44b5b94e12..35bb586ba13229f084279f9e06e7c1f79af4e787 100644
--- a/media/audio/audio_manager.h
+++ b/media/audio/audio_manager.h
@@ -145,6 +145,21 @@ class MEDIA_EXPORT AudioManager {
   virtual void RemoveOutputDeviceChangeListener(
       AudioDeviceListener* listener) = 0;
 
+  // It is possible to register listeners for logging of important state
+  // changes. These are mainly intended for input streams and is used to track
+  // down issues related to failing captured audio (http://crbug.com/404884).
+  // The typical repsonse to receiving this callback is to add the information
+  // to some sort of log file.
+  // TODO(henrika): remove these when we have understood why audio is sometimes
+  // not captured as it should. See http://crbug.com/405449.
+  class StateChangeListener {
+   public:
+    virtual void OnStateChange(const std::string& state) = 0;
+  };
+
+  virtual void AddStateChangeListener(StateChangeListener* listener) = 0;
+  virtual void RemoveStateChangeListener(StateChangeListener* listener) = 0;
+
   // Returns the default output hardware audio parameters for opening output
   // streams. It is a convenience interface to
   // AudioManagerBase::GetPreferredOutputStreamParameters and each AudioManager