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..ba2f7a85da5f140431ef6c7156413f9f7274c544 100644
--- a/media/blink/webaudiosourceprovider_impl.h
+++ b/media/blink/webaudiosourceprovider_impl.h
@@ -69,13 +69,17 @@ class MEDIA_BLINK_EXPORT WebAudioSourceProviderImpl
                           const OutputDeviceStatusCB& callback) override;
 
   // These methods allow a client to get a copy of the rendered audio.
-  void SetCopyAudioCallback(const CopyAudioCB& callback);
-  void ClearCopyAudioCallback();
+  virtual void SetCopyAudioCallback(const CopyAudioCB& callback);

[miu, 2016/05/13 23:40:35]

Why are these methods being made virtual?

[mcasas, 2016/05/14 02:23:47]

For MockWebAudioSourceProvider in 
html_audio_element_capturer_unittest.cc

+  virtual void ClearCopyAudioCallback();
+  base::WeakPtr<WebAudioSourceProviderImpl> AsWeakPtr() {
+    return weak_factory_.GetWeakPtr();
+  }
 
- private:
+ protected:
   friend class WebAudioSourceProviderImplTest;
   ~WebAudioSourceProviderImpl() override;
 
+ private:
   // Calls setFormat() on |client_| from the Blink renderer thread.
   void OnSetFormat();