Use "application default" audio device as default PulseAudio device.

media/audio/pulse/pulse_input.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.
 
 #ifndef MEDIA_AUDIO_PULSE_PULSE_INPUT_H_
 #define MEDIA_AUDIO_PULSE_PULSE_INPUT_H_
 
 #include <pulse/pulseaudio.h>
 #include <stddef.h>
 #include <string>
@@ skipping 34 matching lines @@
   // PulseAudio Callbacks.
   static void ReadCallback(pa_stream* handle, size_t length, void* user_data);
   static void StreamNotifyCallback(pa_stream* stream, void* user_data);
   static void VolumeCallback(pa_context* context, const pa_source_info* info,
                              int error, void* user_data);
   static void MuteCallback(pa_context* context,
                            const pa_source_info* info,
                            int error,
                            void* user_data);
 
-  // pa_context_get_server_info callback. It's used by
-  // GetSystemDefaultInputDevice to set |default_system_device_name_| to the
-  // default system input device.
-  static void GetSystemDefaultInputDeviceCallback(pa_context* context,
-                                                  const pa_server_info* info,
-                                                  void* user_data);
-
-  // Get default system input device for the input stream.
-  void GetSystemDefaultInputDevice();
-
   // Helper for the ReadCallback.
   void ReadData();
 
   // Utility method used by GetVolume() and IsMuted().
   bool GetSourceInformation(pa_source_info_cb_t callback);
 
   AudioManagerPulse* audio_manager_;
   AudioInputCallback* callback_;
-  const std::string device_name_;
-  // The name of the system default device. Set by
-  // GetSystemDefaultInputDeviceCallback if |device_name_| is set to be the
-  // default device.
-  std::string default_system_device_name_;
-
+  std::string device_name_;
   AudioParameters params_;
   int channels_;
   double volume_;
   bool stream_started_;
 
   // Set to true in IsMuted() if user has muted the selected microphone in the
   // sound settings UI.
   bool muted_;
 
   // Holds the data from the OS.
   AudioBlockFifo fifo_;
 
   // PulseAudio API structs.
   pa_threaded_mainloop* pa_mainloop_; // Weak.
   pa_context* pa_context_;  // Weak.
   pa_stream* handle_;
 
   base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(PulseAudioInputStream);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_AUDIO_PULSE_PULSE_INPUT_H_