Add a method to tab_utils.h to find out whether a tab is playing audio.

chrome/browser/media/audio_stream_indicator.h

+// Copyright (c) 2012 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 CHROME_BROWSER_MEDIA_AUDIO_STREAM_INDICATOR_H_
+#define CHROME_BROWSER_MEDIA_AUDIO_STREAM_INDICATOR_H_
+
+#include <set>
+
+#include "base/memory/ref_counted.h"
+
+namespace content {
+class WebContents;
+}
+
+class AudioStreamIndicator
+    : public base::RefCountedThreadSafe<AudioStreamIndicator> {
+ public:
+  AudioStreamIndicator();
+
+  // This method should be called on the IO thread.
+  void UpdateWebContentsStatus(int render_process_id,
+                               int render_view_id,
+                               bool playing);
+
+  // This method should be called on the IO thread.
+  bool IsPlayingAudio(content::WebContents* contents);
+
+ private:
+  struct RenderViewId {
+    RenderViewId(int render_process_id,
+                 int render_view_id);
+
+    // Required to use this struct in the std::multiset below.
+    bool operator<(const RenderViewId& other) const;
+
+    int render_process_id;
+    int render_view_id;
+  };
+
+  friend class base::RefCountedThreadSafe<AudioStreamIndicator>;
+  virtual ~AudioStreamIndicator();
+
+  void UpdateWebContentsStatusOnUIThread(int render_process_id,
+                                         int render_view_id,
+                                         bool playing);
+
+  // The set of RenderViews that currently have a stream playing (a multiset
+  // because each RenderView might have more than one stream).
+  std::multiset<RenderViewId> audio_streams_;
+};
+
+#endif  // CHROME_BROWSER_MEDIA_AUDIO_STREAM_INDICATOR_H_