Only send the FrameSinkId to client when it is necessary

ui/aura/mus/mus_context_factory.cc

Index: ui/aura/mus/mus_context_factory.cc
diff --git a/ui/aura/mus/mus_context_factory.cc b/ui/aura/mus/mus_context_factory.cc
index 9517875318f35ee39d05ef00313a8b7970cf1c18..b904bf589366f85ed160ae236ae71e244f1dc48e 100644
--- a/ui/aura/mus/mus_context_factory.cc
+++ b/ui/aura/mus/mus_context_factory.cc
@@ -26,18 +26,10 @@ void MusContextFactory::OnEstablishedGpuChannel(
       WindowTreeHost::GetForAcceleratedWidget(compositor->widget());
   WindowPortMus* window_port = WindowPortMus::Get(host->window());
   DCHECK(window_port);
-  window_port->RequestCompositorFrameSink(
-      gpu_->CreateContextProvider(std::move(gpu_channel)),
-      gpu_->gpu_memory_buffer_manager(),
-      base::Bind(&MusContextFactory::OnCompositorFrameSinkAvailable,
-                 weak_ptr_factory_.GetWeakPtr(), compositor));
-}
-
-void MusContextFactory::OnCompositorFrameSinkAvailable(
-    base::WeakPtr<ui::Compositor> compositor,
-    std::unique_ptr<cc::CompositorFrameSink> compositor_frame_sink) {
-  if (!compositor)
-    return;
+  std::unique_ptr<cc::CompositorFrameSink> compositor_frame_sink =
+      window_port->RequestCompositorFrameSink(
+          gpu_->CreateContextProvider(std::move(gpu_channel)),
+          gpu_->gpu_memory_buffer_manager());
   compositor->SetCompositorFrameSink(std::move(compositor_frame_sink));
 }