Interface for requestSources through UserMediaController/Client.

public/web/WebUserMediaClient.h

Index: public/web/WebUserMediaClient.h
diff --git a/public/web/WebUserMediaClient.h b/public/web/WebUserMediaClient.h
index 1af35e6fde346dcc73877695d5bc5bddf1785841..76a279889650deea01f09167c0ca1ada3104d98a 100644
--- a/public/web/WebUserMediaClient.h
+++ b/public/web/WebUserMediaClient.h
@@ -34,6 +34,7 @@
 namespace blink {
 
 class WebMediaDevicesRequest;
+class WebMediaStreamTrackSourcesRequest;
 class WebUserMediaRequest;
 template <typename T> class WebVector;
 
@@ -45,6 +46,7 @@ public:
     virtual void cancelUserMediaRequest(const WebUserMediaRequest&) = 0;
     virtual void requestMediaDevices(const WebMediaDevicesRequest&) = 0;
     virtual void cancelMediaDevicesRequest(const WebMediaDevicesRequest&) = 0;
+    virtual void requestSources(const WebMediaStreamTrackSourcesRequest&) = 0;
 };
 
 } // namespace blink