MediaCaptureFromElement: add support for audio captureStream().

media/blink/webaudiosourceprovider_impl.cc

Index: media/blink/webaudiosourceprovider_impl.cc
diff --git a/media/blink/webaudiosourceprovider_impl.cc b/media/blink/webaudiosourceprovider_impl.cc
index 3f052dbeb6f5a8f9759964cb534635f5e19ebd79..31bb5aa11b69a46ee5fe1507fd9290907117c65b 100644
--- a/media/blink/webaudiosourceprovider_impl.cc
+++ b/media/blink/webaudiosourceprovider_impl.cc
@@ -233,6 +233,10 @@ void WebAudioSourceProviderImpl::Initialize(const AudioParameters& params,
 void WebAudioSourceProviderImpl::SetCopyAudioCallback(
     const CopyAudioCB& callback) {
   DCHECK(!callback.is_null());
+
+  // Use |sink_lock_| to protect |tee_filter_| too since they go in lockstep.
+  base::AutoLock auto_lock(sink_lock_);
+
   DCHECK(tee_filter_);
   tee_filter_->set_copy_audio_bus_callback(callback);
 }
@@ -242,6 +246,10 @@ void WebAudioSourceProviderImpl::ClearCopyAudioCallback() {
   tee_filter_->set_copy_audio_bus_callback(CopyAudioCB());
 }
 
+int WebAudioSourceProviderImpl::RenderForTesting(AudioBus* audio_bus) {
+  return tee_filter_->Render(audio_bus, 0, 0);
+}
+
 void WebAudioSourceProviderImpl::OnSetFormat() {
   base::AutoLock auto_lock(sink_lock_);
   if (!client_)
@@ -251,10 +259,6 @@ void WebAudioSourceProviderImpl::OnSetFormat() {
   client_->setFormat(tee_filter_->channels(), tee_filter_->sample_rate());
 }
 
-int WebAudioSourceProviderImpl::RenderForTesting(AudioBus* audio_bus) {
-  return tee_filter_->Render(audio_bus, 0, 0);
-}
-
 int WebAudioSourceProviderImpl::TeeFilter::Render(AudioBus* audio_bus,
                                                   uint32_t delay_milliseconds,
                                                   uint32_t frames_skipped) {