Add support for switching the audio output device for HTMLMediaElements.

media/audio/audio_output_device.h

Index: media/audio/audio_output_device.h
diff --git a/media/audio/audio_output_device.h b/media/audio/audio_output_device.h
index ca11b80d9900dfc0d52ac00d621522aa18abf9d0..be60af1ea8bd8838efb018303f678ff09b0898c6 100644
--- a/media/audio/audio_output_device.h
+++ b/media/audio/audio_output_device.h
@@ -58,8 +58,12 @@
 #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"
@@ -95,6 +99,9 @@ class MEDIA_EXPORT AudioOutputDevice
   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.
@@ -102,6 +109,8 @@ class MEDIA_EXPORT AudioOutputDevice
   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:
@@ -129,6 +138,9 @@ class MEDIA_EXPORT AudioOutputDevice
   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.
@@ -171,6 +183,11 @@ class MEDIA_EXPORT AudioOutputDevice
   // 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);
 };