Interface for requestSources through UserMediaController/Client.

Source/modules/mediastream/UserMediaClient.h

Index: Source/modules/mediastream/UserMediaClient.h
diff --git a/Source/modules/mediastream/UserMediaClient.h b/Source/modules/mediastream/UserMediaClient.h
index 7d607fffb95a5255019b8e44594228100baec3e9..f3f91591f496141b92208d954f3ac22cdddcede3 100644
--- a/Source/modules/mediastream/UserMediaClient.h
+++ b/Source/modules/mediastream/UserMediaClient.h
@@ -33,6 +33,7 @@
 
 #include "modules/mediastream/MediaDevicesRequest.h"
 #include "modules/mediastream/UserMediaRequest.h"
+#include "platform/mediastream/MediaStreamTrackSourcesRequest.h"
 
 namespace blink {
 
@@ -44,6 +45,7 @@ public:
     virtual void cancelUserMediaRequest(UserMediaRequest*) = 0;
     virtual void requestMediaDevices(MediaDevicesRequest*) = 0;
     virtual void cancelMediaDevicesRequest(MediaDevicesRequest*) = 0;
+    virtual void requestSources(MediaStreamTrackSourcesRequest*) = 0;
 
 protected:
     virtual ~UserMediaClient() { }