Communicate audio state to renderer process on Android.

content/browser/media/audio_stream_monitor.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_MEDIA_AUDIO_STREAM_MONITOR_H_
 #define CONTENT_BROWSER_MEDIA_AUDIO_STREAM_MONITOR_H_
 
 #include <map>
 #include <utility>
 
@@ skipping 16 matching lines @@
 class WebContents;
 
 // Repeatedly polls audio streams for their power levels, and "debounces" the
 // information into a simple, binary "was recently audible" result for the audio
 // indicators in the tab UI.  The debouncing logic is to: 1) Turn on immediately
 // when sound is audible; and 2) Hold on for X amount of time after sound has
 // gone silent, then turn off.  Said another way, we don't want tab indicators
 // 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() {
+  // 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();
   }
 
   // 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
   // the killing of tabs making sounds).
   bool WasRecentlyAudible() const;
 
   // Returns true if the audio is currently audible from the given WebContents.
@@ skipping 56 matching lines @@
 
   // Called by |poll_timer_| to sample the power levels from each of the streams
   // playing in the tab.
   void Poll();
 
   // Compares last known indicator state with what it should be, and triggers UI
   // updates through |web_contents_| if needed.  When the indicator is turned
   // 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.

[miu, 2016/11/15 22:06:04]

This can go on the above line.

[altimin, 2016/11/16 12:52:46]

Done.

+  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_;
 
   // Note: |clock_| is always |&default_tick_clock_|, except during unit
   // testing.
   base::DefaultTickClock default_tick_clock_;
   base::TickClock* const clock_;
 
   // Confirms single-threaded access in debug builds.
@@ skipping 15 matching lines @@
   // Whether the WebContents is currently audible.
   bool is_audible_;
 
   // Calls Poll() at regular intervals while |poll_callbacks_| is non-empty.
   base::RepeatingTimer poll_timer_;
 
   // Started only when an indicator is toggled on, to turn it off again in the
   // 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);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_MEDIA_AUDIO_STREAM_MONITOR_H_