Let default device in PulseAudio be the system default device

media/audio/pulse/pulse_input.cc

Index: media/audio/pulse/pulse_input.cc
diff --git a/media/audio/pulse/pulse_input.cc b/media/audio/pulse/pulse_input.cc
index 8d4aeea2079d201a69e52fb48e4344680c467d70..db13935d23aad80b3d34e1d94f851ba99a22f148 100644
--- a/media/audio/pulse/pulse_input.cc
+++ b/media/audio/pulse/pulse_input.cc
@@ -51,8 +51,15 @@ PulseAudioInputStream::~PulseAudioInputStream() {
 bool PulseAudioInputStream::Open() {
   DCHECK(thread_checker_.CalledOnValidThread());
   AutoPulseLock auto_lock(pa_mainloop_);
+  std::string device_name_to_use = device_name_;
+  if (device_name_ == AudioManagerBase::kDefaultDeviceId) {
+    GetSystemDefaultInputDevice();
+    device_name_to_use = default_system_device_name_;
+  }
+
   if (!pulse::CreateInputStream(pa_mainloop_, pa_context_, &handle_, params_,
-                                device_name_, &StreamNotifyCallback, this)) {
+                                device_name_to_use, &StreamNotifyCallback,
+                                this)) {
     return false;
   }
 
@@ -268,6 +275,26 @@ void PulseAudioInputStream::StreamNotifyCallback(pa_stream* s,
   pa_threaded_mainloop_signal(stream->pa_mainloop_, 0);
 }
 
+// static, used by pa_context_get_server_info.
+void PulseAudioInputStream::GetSystemDefaultInputDeviceCallback(
+    pa_context* context,
+    const pa_server_info* info,
+    void* user_data) {
+  media::PulseAudioInputStream* stream =
+      static_cast<media::PulseAudioInputStream*>(user_data);
+  stream->default_system_device_name_ = info->default_source_name;
+  pa_threaded_mainloop_signal(stream->pa_mainloop_, 0);
+}
+
+void PulseAudioInputStream::GetSystemDefaultInputDevice() {
+  DCHECK(pa_mainloop_);
+  DCHECK(pa_context_);
+  pa_operation* operation = pa_context_get_server_info(
+      pa_context_, PulseAudioInputStream::GetSystemDefaultInputDeviceCallback,
+      this);
+  WaitForOperationCompletion(pa_mainloop_, operation);
+}
+
 void PulseAudioInputStream::ReadData() {
   uint32_t hardware_delay = pulse::GetHardwareLatencyInBytes(
       handle_, params_.sample_rate(), params_.GetBytesPerFrame());