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..eea08ca158dfb834e12961cb9e30f23d20625f68 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_;