Only send the FrameSinkId to client when it is necessary

ui/aura/mus/mus_context_factory.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/aura/mus/mus_context_factory.h"
 
 #include "base/command_line.h"
 #include "base/memory/ptr_util.h"
 #include "cc/base/switches.h"
 #include "services/ui/public/cpp/gpu/gpu.h"
@@ skipping 20 matching lines @@
 
 void MusContextFactory::OnEstablishedGpuChannel(
     base::WeakPtr<ui::Compositor> compositor,
     scoped_refptr<gpu::GpuChannelHost> gpu_channel) {
   if (!compositor)
     return;
   WindowTreeHost* host =
       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));
 }
 
 void MusContextFactory::CreateCompositorFrameSink(
     base::WeakPtr<ui::Compositor> compositor) {
   gpu_->EstablishGpuChannel(
       base::Bind(&MusContextFactory::OnEstablishedGpuChannel,
                  weak_ptr_factory_.GetWeakPtr(), compositor));
 }
 
@@ skipping 17 matching lines @@
 
 cc::TaskGraphRunner* MusContextFactory::GetTaskGraphRunner() {
   return raster_thread_helper_.task_graph_runner();
 }
 
 const cc::RendererSettings& MusContextFactory::GetRendererSettings() const {
   return renderer_settings_;
 }
 
 }  // namespace aura