Only send the FrameSinkId to client when it is necessary

ui/aura/mus/mus_context_factory.h

Index: ui/aura/mus/mus_context_factory.h
diff --git a/ui/aura/mus/mus_context_factory.h b/ui/aura/mus/mus_context_factory.h
index 11b2065e90fad78626094050fc10714f776a5cfd..573e6bbf42b88833e589f3ab61bb1a76519fe49b 100644
--- a/ui/aura/mus/mus_context_factory.h
+++ b/ui/aura/mus/mus_context_factory.h
@@ -37,10 +37,6 @@ class AURA_EXPORT MusContextFactory : public ui::ContextFactory {
   void OnEstablishedGpuChannel(base::WeakPtr<ui::Compositor> compositor,
                                scoped_refptr<gpu::GpuChannelHost> gpu_channel);
 
-  void OnCompositorFrameSinkAvailable(
-      base::WeakPtr<ui::Compositor> compositor,
-      std::unique_ptr<cc::CompositorFrameSink> compositor_frame_sink);
-
   // ContextFactory:
   void CreateCompositorFrameSink(
       base::WeakPtr<ui::Compositor> compositor) override;