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

cc/surfaces/display.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_DISPLAY_H_
 #define CC_SURFACES_DISPLAY_H_
 
 #include "base/memory/scoped_ptr.h"
 
 #include "cc/output/output_surface_client.h"
 #include "cc/output/renderer.h"
 #include "cc/surfaces/surface_aggregator.h"
 #include "cc/surfaces/surface_client.h"
+#include "cc/surfaces/surface_id.h"
 #include "cc/surfaces/surfaces_export.h"
 
 namespace gfx {
 class Size;
 }
 
 namespace cc {
 
 class DirectRenderer;
 class DisplayClient;
 class OutputSurface;
 class ResourceProvider;
 class SharedBitmapManager;
 class Surface;
 class SurfaceManager;
 
 class CC_SURFACES_EXPORT Display : public SurfaceClient,
                                    public OutputSurfaceClient,
                                    public RendererClient {
  public:
   Display(DisplayClient* client,
           SurfaceManager* manager,
           SharedBitmapManager* bitmap_manager);
   virtual ~Display();
 
   void Resize(const gfx::Size& new_size);
   bool Draw();
 
-  int CurrentSurfaceID();
+  SurfaceId CurrentSurfaceId();
 
   // OutputSurfaceClient implementation.
   virtual void DeferredInitialize() OVERRIDE {}
   virtual void ReleaseGL() OVERRIDE {}
   virtual void CommitVSyncParameters(base::TimeTicks timebase,
                                      base::TimeDelta interval) OVERRIDE {}
   virtual void SetNeedsRedrawRect(const gfx::Rect& damage_rect) OVERRIDE {}
   virtual void BeginFrame(const BeginFrameArgs& args) OVERRIDE {}
   virtual void DidSwapBuffers() OVERRIDE {}
   virtual void DidSwapBuffersComplete() OVERRIDE {}
@@ skipping 27 matching lines @@
   scoped_ptr<ResourceProvider> resource_provider_;
   scoped_ptr<DirectRenderer> renderer_;
   int child_id_;
 
   DISALLOW_COPY_AND_ASSIGN(Display);
 };
 
 }  // namespace cc
 
 #endif  // CC_SURFACES_DISPLAY_H_