Audio indicator: cross platform drawing and animation

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 <map>
 #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,
                                int stream_id,
                                bool playing);
 
-  // This method should be called on the IO thread.
+  // This method should be called on the UI 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,
                                          int stream_id,
                                          bool playing);
 
   // A map from RenderViews to sets of streams playing in them (each RenderView
   // might have more than one stream).
   std::map<RenderViewId, std::set<int> > audio_streams_;
 };
 
 #endif  // CHROME_BROWSER_MEDIA_AUDIO_STREAM_INDICATOR_H_