Make tab audible and muted states and cause available for an extension API

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>
 
 #include "base/callback_forward.h"
 #include "base/threading/thread_checker.h"
 #include "base/time/default_tick_clock.h"
 #include "base/time/time.h"
 #include "base/timer/timer.h"
 #include "build/build_config.h"
 #include "content/common/content_export.h"
 #include "media/audio/audio_output_controller.h"
 
 namespace base {
 class TickClock;
 }
 
 namespace content {
-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.
 //
 // Each WebContentsImpl owns an AudioStreamMonitor.
 class CONTENT_EXPORT AudioStreamMonitor {
  public:
-  explicit AudioStreamMonitor(WebContents* contents);
+  using AudibleChangeCallback = base::Callback<void(bool)>;
+
+  explicit AudioStreamMonitor(const AudibleChangeCallback& callback);
   ~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
@@ 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();
 
-  // The WebContents instance instance to receive indicator toggle
-  // notifications.  This pointer should be valid for the lifetime of
-  // AudioStreamMonitor.
-  WebContents* const web_contents_;
+  // The Callback to run to receive indicator toggle notifications.
+  const AudibleChangeCallback audible_change_callback_;
 
   // 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.
   base::ThreadChecker thread_checker_;
 
   // The callbacks to read power levels for each stream.  Only playing (i.e.,
@@ skipping 15 matching lines @@
   // Started only when an indicator is toggled on, to turn it off again in the
   // future.
   base::OneShotTimer<AudioStreamMonitor> off_timer_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioStreamMonitor);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_MEDIA_AUDIO_STREAM_MONITOR_H_