Wire up the output device id and provide an implementation on Windows.

media/audio/audio_output_controller.h

Index: media/audio/audio_output_controller.h
diff --git a/media/audio/audio_output_controller.h b/media/audio/audio_output_controller.h
index 38a2c03f590faa18dd9c2ca65cf559da6feff23b..387214e1d0ce3c7a3197dab88079784d12bcb147 100644
--- a/media/audio/audio_output_controller.h
+++ b/media/audio/audio_output_controller.h
@@ -101,10 +101,14 @@ class MEDIA_EXPORT AudioOutputController
   // thread, and if this is successful, the |event_handler| will receive an
   // OnCreated() call from the same audio manager thread.  |audio_manager| must
   // outlive AudioOutputController.
+  // The |output_device_id| can be either empty (default device) or specify a
+  // specific hardware device for audio output.  The |input_device_id| is
+  // used only for unified audio when opening up input and output at the same
+  // time (controlled by |params.input_channel_count()|).
   static scoped_refptr<AudioOutputController> Create(
       AudioManager* audio_manager, EventHandler* event_handler,
-      const AudioParameters& params, const std::string& input_device_id,
-      SyncReader* sync_reader);
+      const AudioParameters& params, const std::string& output_device_id,
+      const std::string& input_device_id, SyncReader* sync_reader);
 
   // Methods to control playback of the stream.
 
@@ -166,6 +170,7 @@ class MEDIA_EXPORT AudioOutputController
 
   AudioOutputController(AudioManager* audio_manager, EventHandler* handler,
                         const AudioParameters& params,
+                        const std::string& output_device_id,
                         const std::string& input_device_id,
                         SyncReader* sync_reader);
 
@@ -198,8 +203,12 @@ class MEDIA_EXPORT AudioOutputController
   const AudioParameters params_;
   EventHandler* const handler_;
 
+  // Specifies the device id of the output device to open or empty for the
+  // default output device.
+  const std::string output_device_id_;
+
   // Used by the unified IO to open the correct input device.
-  std::string input_device_id_;
+  const std::string input_device_id_;
 
   AudioOutputStream* stream_;