Add support for switching the audio output device for HTMLMediaElements.

media/audio/audio_output_device.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.
 //
 // Audio rendering unit utilizing audio output stream provided by browser
 // process through IPC.
 //
 // Relationship of classes.
 //
 //  AudioOutputController                AudioOutputDevice
@@ skipping 40 matching lines @@
 //    turn calls AudioRendererSink::RenderCallback which feeds audio samples to
 //    the audio layer in the browser process using sync sockets and shared
 //    memory.
 //
 // Implementation notes:
 // - The user must call Stop() before deleting the class instance.
 
 #ifndef MEDIA_AUDIO_AUDIO_OUTPUT_DEVICE_H_
 #define MEDIA_AUDIO_AUDIO_OUTPUT_DEVICE_H_
 
+#include <map>
+#include <string>
+
 #include "base/basictypes.h"
 #include "base/bind.h"
+#include "base/callback.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/shared_memory.h"
 #include "media/audio/audio_device_thread.h"
 #include "media/audio/audio_output_ipc.h"
 #include "media/audio/audio_parameters.h"
 #include "media/audio/scoped_task_runner_observer.h"
 #include "media/base/audio_renderer_sink.h"
 #include "media/base/media_export.h"
 
 namespace media {
@@ skipping 15 matching lines @@
                                int session_id);
 
   // AudioRendererSink implementation.
   void Initialize(const AudioParameters& params,
                   RenderCallback* callback) override;
   void Start() override;
   void Stop() override;
   void Play() override;
   void Pause() override;
   bool SetVolume(double volume) override;
+  void SwitchOutputDevice(const std::string& device_id,
+                          const GURL& security_origin,
+                          const base::Callback<void(int)>& callback) override;
 
   // Methods called on IO thread ----------------------------------------------
   // AudioOutputIPCDelegate methods.
   void OnStateChanged(AudioOutputIPCDelegate::State state) override;
   void OnStreamCreated(base::SharedMemoryHandle handle,
                        base::SyncSocket::Handle socket_handle,
                        int length) override;
+  void OnDeviceSwitched(int request_id,
+                        AudioOutputIPCDelegate::DeviceSwitchResult) override;
   void OnIPCClosed() override;
 
  protected:
   // Magic required by ref_counted.h to avoid any code deleting the object
   // accidentally while there are references to it.
   friend class base::RefCountedThreadSafe<AudioOutputDevice>;
   ~AudioOutputDevice() override;
 
  private:
   // Note: The ordering of members in this enum is critical to correct behavior!
   enum State {
     IPC_CLOSED,  // No more IPCs can take place.
     IDLE,  // Not started.
     CREATING_STREAM,  // Waiting for OnStreamCreated() to be called back.
     PAUSED,  // Paused.  OnStreamCreated() has been called.  Can Play()/Stop().
     PLAYING,  // Playing back.  Can Pause()/Stop().
   };
 
   // Methods called on IO thread ----------------------------------------------
   // The following methods are tasks posted on the IO thread that need to
   // be executed on that thread.  They use AudioOutputIPC to send IPC messages
   // upon state changes.
   void CreateStreamOnIOThread(const AudioParameters& params);
   void PlayOnIOThread();
   void PauseOnIOThread();
   void ShutDownOnIOThread();
   void SetVolumeOnIOThread(double volume);
+  void SwitchOutputDeviceOnIOThread(const std::string& device_id,
+                                    const GURL& security_origin,
+                                    const base::Callback<void(int)>& callback);
 
   // base::MessageLoop::DestructionObserver implementation for the IO loop.
   // If the IO loop dies before we do, we shut down the audio thread from here.
   void WillDestroyCurrentMessageLoop() override;
 
   AudioParameters audio_parameters_;
 
   RenderCallback* callback_;
 
   // A pointer to the IPC layer that takes care of sending requests over to
@@ skipping 22 matching lines @@
   scoped_ptr<AudioOutputDevice::AudioThreadCallback> audio_callback_;
 
   // Temporary hack to ignore OnStreamCreated() due to the user calling Stop()
   // so we don't start the audio thread pointing to a potentially freed
   // |callback_|.
   //
   // TODO(scherkus): Replace this by changing AudioRendererSink to either accept
   // the callback via Start(). See http://crbug.com/151051 for details.
   bool stopping_hack_;
 
+  // Pending SwitchOutputDevice requests
+  std::map<int, base::Callback<void(int)>> switch_requests_;

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

When is it appropriate to have multiple switch requests in-progress?  It seems
only the last switch request should succeed, so maybe just keep track of that
one and run the callbacks with an abort status code for all the prior ones?

+  int next_switch_request_id_;
+  int AddSwitchRequest(const base::Callback<void(int)>& callback);
+
   DISALLOW_COPY_AND_ASSIGN(AudioOutputDevice);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_AUDIO_AUDIO_OUTPUT_DEVICE_H_