Add support for switching the audio output device for HTMLMediaElements.

media/base/audio_renderer_sink.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 MEDIA_BASE_AUDIO_RENDERER_SINK_H_
 #define MEDIA_BASE_AUDIO_RENDERER_SINK_H_
 
+#include <string>
 #include <vector>
+
 #include "base/basictypes.h"
+#include "base/callback.h"
 #include "base/logging.h"
 #include "base/memory/ref_counted.h"
 #include "media/audio/audio_parameters.h"
 #include "media/base/audio_bus.h"
 #include "media/base/media_export.h"
+#include "url/gurl.h"
 
 namespace media {
 
 // AudioRendererSink is an interface representing the end-point for
 // rendered audio.  An implementation is expected to
 // periodically call Render() on a callback object.
 
 class AudioRendererSink
     : public base::RefCountedThreadSafe<media::AudioRendererSink> {
  public:
@@ skipping 24 matching lines @@
   // Pauses playback.
   virtual void Pause() = 0;
 
   // Resumes playback after calling Pause().
   virtual void Play() = 0;
 
   // Sets the playback volume, with range [0.0, 1.0] inclusive.
   // Returns |true| on success.
   virtual bool SetVolume(double volume) = 0;
 
+  // Switches the audio output device.

[miu, 2015/06/03 21:01:01]

The documentation here is insufficient: Please clarify what the integer argument
to the callback is supposed to be.  Better yet, maybe you should:

  // Callback run with <<EXPLANATION OF INT HERE>> when the output device switch
request has completed.
  using SwitchOutputDeviceDoneCallback = base::Callback<void(int)>;

Also, the int argument should probably be an enum instead...

+  virtual void SwitchOutputDevice(
+      const std::string& device_id,
+      const GURL& security_origin,
+      const base::Callback<void(int)>& callback) = 0;
+
  protected:
   friend class base::RefCountedThreadSafe<AudioRendererSink>;
   virtual ~AudioRendererSink() {}
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_AUDIO_RENDERER_SINK_H_