Reland: MediaCaptureFromElement: add support for audio captureStream().

media/blink/webaudiosourceprovider_impl.h

Index: media/blink/webaudiosourceprovider_impl.h
diff --git a/media/blink/webaudiosourceprovider_impl.h b/media/blink/webaudiosourceprovider_impl.h
index 6bf3b0aa9e379b9811e06598a53c97186fb74b47..196d2ca90f92c3616147f6fff3d702e7305be568 100644
--- a/media/blink/webaudiosourceprovider_impl.h
+++ b/media/blink/webaudiosourceprovider_impl.h
@@ -72,6 +72,8 @@ class MEDIA_BLINK_EXPORT WebAudioSourceProviderImpl
   void SetCopyAudioCallback(const CopyAudioCB& callback);
   void ClearCopyAudioCallback();
 
+  int RenderForTesting(AudioBus* audio_bus);
+
  private:
   friend class WebAudioSourceProviderImplTest;
   ~WebAudioSourceProviderImpl() override;
@@ -79,8 +81,6 @@ class MEDIA_BLINK_EXPORT WebAudioSourceProviderImpl
   // Calls setFormat() on |client_| from the Blink renderer thread.
   void OnSetFormat();
 
-  int RenderForTesting(AudioBus* audio_bus);
-
   // Used to keep the volume across reconfigurations.
   double volume_;
 
@@ -100,7 +100,7 @@ class MEDIA_BLINK_EXPORT WebAudioSourceProviderImpl
 
   // An inner class acting as a T filter where actual data can be tapped.
   class TeeFilter;
-  std::unique_ptr<TeeFilter> tee_filter_;
+  const std::unique_ptr<TeeFilter> tee_filter_;
 
   // NOTE: Weak pointers must be invalidated before all other member variables.
   base::WeakPtrFactory<WebAudioSourceProviderImpl> weak_factory_;