Bug 1293472 (Part 1) - Make it possible to seek DecodedSurfaces. r=dholbert

image/DecodedSurfaceProvider.cpp

@@ -53,8 +53,11 @@ DecodedSurfaceProvider::DropImageReference()
 }
 
 DrawableFrameRef
-DecodedSurfaceProvider::DrawableRef()
+DecodedSurfaceProvider::DrawableRef(size_t aFrame)
 {
+  MOZ_ASSERT(aFrame == 0,
+             "Requesting an animation frame from a DecodedSurfaceProvider?");
+
   // We depend on SurfaceCache::SurfaceAvailable() to provide synchronization
   // for methods that touch |mSurface|; after SurfaceAvailable() is called,
   // |mSurface| should be non-null and shouldn't be mutated further until we get