Aura-Mus: Enable Surface Synchronization behind flag

ui/aura/mus/window_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_MUS_H_
 #define UI_AURA_MUS_WINDOW_MUS_H_
 
 #include <stdint.h>
 
 #include <string>
@@ skipping 71 matching lines @@
   virtual void SetVisibleFromServer(bool visible) = 0;
   virtual void SetOpacityFromServer(float opacity) = 0;
   virtual void SetPredefinedCursorFromServer(ui::mojom::CursorType cursor) = 0;
   virtual void SetPropertyFromServer(const std::string& property_name,
                                      const std::vector<uint8_t>* data) = 0;
   virtual void SetFrameSinkIdFromServer(
       const cc::FrameSinkId& frame_sink_id) = 0;
   virtual const cc::LocalSurfaceId& GetOrAllocateLocalSurfaceId(
       const gfx::Size& new_size) = 0;
   virtual void SetPrimarySurfaceInfo(const cc::SurfaceInfo& surface_info) = 0;
+  virtual void SetFallbackSurfaceInfo(const cc::SurfaceInfo& surface_info) = 0;
   // The window was deleted on the server side. DestroyFromServer() should
   // result in deleting |this|.
   virtual void DestroyFromServer() = 0;
   virtual void AddTransientChildFromServer(WindowMus* child) = 0;
   virtual void RemoveTransientChildFromServer(WindowMus* child) = 0;
   // Called when a window was added/removed as a transient child.
   virtual ChangeSource OnTransientChildAdded(WindowMus* child) = 0;
   virtual ChangeSource OnTransientChildRemoved(WindowMus* child) = 0;
 
   // Returns the currently used cc::LocalSurfaceId to embed this Window. Local
@@ skipping 29 matching lines @@
 
   void set_server_id(Id id) { server_id_ = id; }
 
   Id server_id_ = kInvalidServerId;
   const WindowMusType window_mus_type_;
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_MUS_WINDOW_MUS_H_