Use a struct for cc::Surface ids for more type safety

cc/surfaces/surface_manager.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 CC_SURFACES_SURFACE_MANAGER_H_
 #define CC_SURFACES_SURFACE_MANAGER_H_
 
 #include "base/containers/hash_tables.h"
 #include "base/macros.h"
+#include "cc/surfaces/surface_id.h"
 #include "cc/surfaces/surfaces_export.h"
 
-namespace gfx { class Size; }
-
 namespace cc {
 class CompositorFrame;
 class Surface;
+class SurfaceClient;
 
 class CC_SURFACES_EXPORT SurfaceManager {
  public:
   SurfaceManager();
   ~SurfaceManager();
 
-  int RegisterAndAllocateIDForSurface(Surface* surface);
-  void DeregisterSurface(int surface_id);
+  SurfaceId RegisterAndAllocateIdForSurface(Surface* surface);
+  void DeregisterSurface(SurfaceId surface_id);
 
-  Surface* GetSurfaceForID(int surface_id);
+  Surface* GetSurfaceForId(SurfaceId surface_id);
 
  private:
   typedef base::hash_map<int, Surface*> SurfaceMap;
   SurfaceMap surface_map_;
 
   int next_surface_id_;
 
   DISALLOW_COPY_AND_ASSIGN(SurfaceManager);
 };
 
 }  // namespace cc
 
 #endif  // CC_SURFACES_SURFACE_MANAGER_H_