Propagate audible state from player to the containing tab

content/browser/media/audio_state_provider.h

+// Copyright 2015 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_STATE_PROVIDER_H_
+#define CONTENT_BROWSER_MEDIA_AUDIO_STATE_PROVIDER_H_
+
+namespace content {
+class WebContents;
+class AudioStreamMonitor;
+
+// This class is associated with a WebContents, and maintains the audible
+// state regarding all the players in it.
+// The audible state is true if at least one player is playing a sound.
+// Whenever the audible state of the WebContents as a whole changes, this
+// class sends a notification to it.
+//
+// Each WebContentsImpl owns an AudioStateProvider
+class AudioStateProvider {
+ public:
+  explicit AudioStateProvider(WebContents* web_contents);
+  virtual ~AudioStateProvider() {}
+
+  // Indicates whether this service is available on the system.
+  virtual bool IsAudioStateAvailable() const = 0;
+
+  // If this provider uses monitoring (i.e. measure the signal),
+  // return its monitor.
+  virtual AudioStreamMonitor* audio_stream_monitor() = 0;
+
+  // Returns true if the WebContents is playing or has recently been
+  // playing the sound.
+  virtual bool WasRecentlyAudible() const;
+
+  void set_was_recently_audible_for_testing(bool value) {
+    was_recently_audible_ = value;
+  }
+
+ protected:
+  // Notify WebContents that the audio state has changed.
+  void Notify(bool new_state);
+
+  // The WebContents instance instance to receive indicator toggle
+  // notifications.  This pointer should be valid for the lifetime of
+  // AudioStreamMonitor.
+  WebContents* const web_contents_;
+
+  // The audio state that is being maintained
+  bool  was_recently_audible_;
+
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_MEDIA_AUDIO_STATE_PROVIDER_H_