mus: Embedder can request and observe BeginFrame for embedded client.

ui/aura/mus/window_tree_client.h

 // Copyright 2014 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_TREE_CLIENT_H_
 #define UI_AURA_MUS_WINDOW_TREE_CLIENT_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 301 matching lines @@
                             size_t current_index,
                             size_t dest_index);
   void OnWindowMusSetVisible(WindowMus* window, bool visible);
   std::unique_ptr<ui::PropertyData> OnWindowMusWillChangeProperty(
       WindowMus* window,
       const void* key);
   void OnWindowMusPropertyChanged(WindowMus* window,
                                   const void* key,
                                   int64_t old_value,
                                   std::unique_ptr<ui::PropertyData> data);
+  void RequestBeginFrames(WindowMus* window,
+                          cc::mojom::FrameSinkObserverPtr observer);
 
   // Callback passed from WmPerformMoveLoop().
   void OnWmMoveLoopCompleted(uint32_t change_id, bool completed);
 
   // Overridden from WindowTreeClient:
   void OnEmbed(
       ClientSpecificId client_id,
       ui::mojom::WindowDataPtr root,
       ui::mojom::WindowTreePtr tree,
       int64_t display_id,
@@ skipping 306 matching lines @@
   gfx::Insets normal_client_area_insets_;
 
   base::WeakPtrFactory<WindowTreeClient> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowTreeClient);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_MUS_WINDOW_TREE_CLIENT_H_