Add support for switching the audio output device for HTMLMediaElements.

media/base/audio_renderer_sink.h

Index: media/base/audio_renderer_sink.h
diff --git a/media/base/audio_renderer_sink.h b/media/base/audio_renderer_sink.h
index fa1ee84c250a10e16eb0db310b38a31cd555c65c..434e9bbca097c8fc60c00a44288338dd4acd64f7 100644
--- a/media/base/audio_renderer_sink.h
+++ b/media/base/audio_renderer_sink.h
@@ -5,13 +5,17 @@
 #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 {
 
@@ -56,6 +60,12 @@ class AudioRendererSink
   // 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() {}