Let default device in PulseAudio be the system default device

media/audio/pulse/pulse_output.h

Index: media/audio/pulse/pulse_output.h
diff --git a/media/audio/pulse/pulse_output.h b/media/audio/pulse/pulse_output.h
index ce9a58914ece8af79409b0c537605e650d59060c..49f6abf28d1106789ab452cf21bffa65a4d0725c 100644
--- a/media/audio/pulse/pulse_output.h
+++ b/media/audio/pulse/pulse_output.h
@@ -20,6 +20,7 @@
 #ifndef MEDIA_AUDIO_PULSE_PULSE_OUTPUT_H_
 #define MEDIA_AUDIO_PULSE_PULSE_OUTPUT_H_
 
+#include <pulse/pulseaudio.h>
 #include <stddef.h>
 
 #include <string>
@@ -63,6 +64,20 @@ class PulseAudioOutputStream : public AudioOutputStream {
   // Called by PulseAudio when it needs more audio data.
   static void StreamRequestCallback(pa_stream* s, size_t len, void* p_this);
 
+  // pa_context_get_server_info callback. It's used by
+  // GetSystemDefaultOutputDevice to set |default_system_device_name_| to the
+  // default system output device.
+  static void GetSystemDefaultOutputDeviceCallback(pa_context* context,
+                                                   const pa_server_info* info,
+                                                   void* user_data);
+
+  // Initialize |pa_mainloop_| and |pa_context_| and prepare them for creating
+  // an output stream.
+  bool InitializeMainloopAndContext();
+
+  // Get default system output device for the output stream.
+  void GetSystemDefaultOutputDevice();
+
   // Fulfill a write request from the write request callback.  Outputs silence
   // if the request could not be fulfilled.
   void FulfillWriteRequest(size_t requested_bytes);
@@ -75,6 +90,10 @@ class PulseAudioOutputStream : public AudioOutputStream {
 
   // The device ID for the device to open.
   const std::string device_id_;
+  // The name of the system default device. Set by
+  // GetSystemDefaultOutputDeviceCallback if |device_id_| is set to be the
+  // default device.
+  std::string default_system_device_name_;
 
   // Audio manager that created us.  Used to report that we've closed.
   AudioManagerBase* manager_;