Only send the FrameSinkId to client when it is necessary

ui/aura/mus/window_port_mus.h

 // Copyright 2016 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.
 
 #ifndef UI_AURA_MUS_WINDOW_PORT_MUS_H_
 #define UI_AURA_MUS_WINDOW_PORT_MUS_H_
 
 #include <stdint.h>
 
 #include <string>
@@ skipping 58 matching lines @@
 
   // Sets whether this window can accept drops, defaults to false.
   void SetCanAcceptDrops(bool can_accept_drops);
 
   // Embeds a new client in this Window. See WindowTreeClient::Embed() for
   // details on arguments.
   void Embed(ui::mojom::WindowTreeClientPtr client,
              uint32_t flags,
              const ui::mojom::WindowTree::EmbedCallback& callback);
 
-  using CompositorFrameSinkCallback =
-      base::Callback<void(std::unique_ptr<cc::CompositorFrameSink>)>;
-  void RequestCompositorFrameSink(
+  std::unique_ptr<cc::CompositorFrameSink> RequestCompositorFrameSink(
       scoped_refptr<cc::ContextProvider> context_provider,
-      gpu::GpuMemoryBufferManager* gpu_memory_buffer_manager,
-      const CompositorFrameSinkCallback& callback);
-
-  void RequestCompositorFrameSinkInternal(
-      scoped_refptr<cc::ContextProvider> context_provider,
-      gpu::GpuMemoryBufferManager* gpu_memory_buffer_manager,
-      const CompositorFrameSinkCallback& callback);
+      gpu::GpuMemoryBufferManager* gpu_memory_buffer_manager);
 
   void AttachCompositorFrameSink(
       std::unique_ptr<ui::ClientCompositorFrameSinkBinding>
           compositor_frame_sink_binding);
 
  private:
   friend class WindowPortMusTestApi;
   friend class WindowTreeClient;
   friend class WindowTreeClientPrivate;
   friend class WindowTreeHostMus;
@@ skipping 174 matching lines @@
 
   Window* window_ = nullptr;
 
   // Used when this window is embedding a client.
   std::unique_ptr<ClientSurfaceEmbedder> client_surface_embedder_;
 
   ServerChangeIdType next_server_change_id_ = 0;
   ServerChanges server_changes_;
 
   cc::FrameSinkId frame_sink_id_;
-  base::Closure pending_compositor_frame_sink_request_;
 
   cc::SurfaceInfo primary_surface_info_;
   cc::SurfaceInfo fallback_surface_info_;
 
   cc::LocalSurfaceId local_surface_id_;
   cc::LocalSurfaceIdAllocator local_surface_id_allocator_;
   gfx::Size last_surface_size_;
 
   ui::CursorData cursor_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowPortMus);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_MUS_WINDOW_PORT_MUS_H_