Communicate audio state to renderer process on Android.

content/browser/media/audio_stream_monitor.h

Index: content/browser/media/audio_stream_monitor.h
diff --git a/content/browser/media/audio_stream_monitor.h b/content/browser/media/audio_stream_monitor.h
index 12f06055c54970fda0d454eae788c1a6346439aa..ced46683efbfb3dcf17b91245bd65ac183fde2f4 100644
--- a/content/browser/media/audio_stream_monitor.h
+++ b/content/browser/media/audio_stream_monitor.h
@@ -34,18 +34,15 @@ class WebContents;
 // to turn on/off repeatedly and annoy the user.  AudioStreamMonitor sends UI
 // update notifications only when needed, but may be queried at any time.
 //
+// When power level monitoring is not available, audibility is approximated
+// with having active audio streams.
+//
 // Each WebContentsImpl owns an AudioStreamMonitor.
 class CONTENT_EXPORT AudioStreamMonitor {
  public:
   explicit AudioStreamMonitor(WebContents* contents);
   ~AudioStreamMonitor();
 
-  // Indicates if audio stream monitoring is available.  It's only available if
-  // AudioOutputController can and will monitor output power levels.
-  static bool monitoring_available() {
-    return media::AudioOutputController::will_monitor_audio_levels();
-  }
-
   // Returns true if audio has recently been audible from the tab.  This is
   // usually called whenever the tab data model is refreshed; but there are
   // other use cases as well (e.g., the OOM killer uses this to de-prioritize
@@ -89,6 +86,13 @@ class CONTENT_EXPORT AudioStreamMonitor {
     kHoldOnMilliseconds = 2000
   };
 
+  // Indicates if monitoring of audio stream power level is available.
+  // It's only available if AudioOutputController can and will monitor
+  // output power levels.
+  static bool power_level_monitoring_available() {
+    return media::AudioOutputController::will_monitor_audio_levels();
+  }
+
   // Helper methods for starting and stopping monitoring which lookup the
   // identified renderer and forward calls to the correct AudioStreamMonitor.
   static void StartMonitoringHelper(
@@ -119,6 +123,11 @@ class CONTENT_EXPORT AudioStreamMonitor {
   // on, |off_timer_| is started to re-invoke this method in the future.
   void MaybeToggle();
 
+  // Helper functions to track number of active streams when power level
+  // monitoring is not available.
+  void OnStreamAdded();
+  void OnStreamRemoved();
+
   // The WebContents instance to receive indicator toggle notifications.  This
   // pointer should be valid for the lifetime of AudioStreamMonitor.
   WebContents* const web_contents_;
@@ -154,6 +163,10 @@ class CONTENT_EXPORT AudioStreamMonitor {
   // future.
   base::OneShotTimer off_timer_;
 
+  // Number of active streams to be used as a proxy for audibility when power
+  // level monitoring is not available.
+  size_t active_streams_;
+
   DISALLOW_COPY_AND_ASSIGN(AudioStreamMonitor);
 };