Adding syncrhonization to PulseAudioOutputStream::SetVolume

media/audio/pulse/pulse_output.cc

Index: media/audio/pulse/pulse_output.cc
diff --git a/media/audio/pulse/pulse_output.cc b/media/audio/pulse/pulse_output.cc
index 3aef9476720106208a92be3cab41ee5e4df0a81b..b5c2d2efb774f93426e76a9265707b7af423a8a9 100644
--- a/media/audio/pulse/pulse_output.cc
+++ b/media/audio/pulse/pulse_output.cc
@@ -227,6 +227,9 @@ void PulseAudioOutputStream::Stop() {
 void PulseAudioOutputStream::SetVolume(double volume) {
   DCHECK(thread_checker_.CalledOnValidThread());
 
+  // Waiting for the main loop lock will ensure outstanding callbacks have
+  // completed and |volume_| is not accessed from them.
+  AutoPulseLock auto_lock(pa_mainloop_);
   volume_ = static_cast<float>(volume);
 }