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

cc/layers/surface_layer_impl.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_LAYERS_SURFACE_LAYER_IMPL_H_
 #define CC_LAYERS_SURFACE_LAYER_IMPL_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "cc/base/cc_export.h"
 #include "cc/layers/layer_impl.h"
+#include "cc/surfaces/surface_id.h"
 
 namespace cc {
 
 class CC_EXPORT SurfaceLayerImpl : public LayerImpl {
  public:
   static scoped_ptr<SurfaceLayerImpl> Create(LayerTreeImpl* tree_impl, int id) {
     return make_scoped_ptr(new SurfaceLayerImpl(tree_impl, id));
   }
   virtual ~SurfaceLayerImpl();
 
-  void SetSurfaceId(int surface_id);
+  void SetSurfaceId(SurfaceId surface_id);
 
   // LayerImpl overrides.
   virtual scoped_ptr<LayerImpl> CreateLayerImpl(LayerTreeImpl* tree_impl)
       OVERRIDE;
   virtual void PushPropertiesTo(LayerImpl* layer) OVERRIDE;
   virtual void AppendQuads(QuadSink* quad_sink,
                            AppendQuadsData* append_quads_data) OVERRIDE;
 
  protected:
   SurfaceLayerImpl(LayerTreeImpl* tree_impl, int id);
 
  private:
   virtual void GetDebugBorderProperties(SkColor* color,
                                         float* width) const OVERRIDE;
   virtual void AsValueInto(base::DictionaryValue* dict) const OVERRIDE;
   virtual const char* LayerTypeAsString() const OVERRIDE;
 
-  int surface_id_;
+  SurfaceId surface_id_;
 
   DISALLOW_COPY_AND_ASSIGN(SurfaceLayerImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_SURFACE_LAYER_IMPL_H_