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

cc/layers/surface_layer_impl.cc

 // 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.
 
 #include "cc/layers/surface_layer_impl.h"
 
 #include "cc/debug/debug_colors.h"
 #include "cc/layers/quad_sink.h"
 #include "cc/quads/surface_draw_quad.h"
 
 namespace cc {
 
 SurfaceLayerImpl::SurfaceLayerImpl(LayerTreeImpl* tree_impl, int id)
-    : LayerImpl(tree_impl, id), surface_id_(0) {}
+    : LayerImpl(tree_impl, id) {
+}
 
 SurfaceLayerImpl::~SurfaceLayerImpl() {}
 
 scoped_ptr<LayerImpl> SurfaceLayerImpl::CreateLayerImpl(
     LayerTreeImpl* tree_impl) {
   return SurfaceLayerImpl::Create(tree_impl, id()).PassAs<LayerImpl>();
 }
 
-void SurfaceLayerImpl::SetSurfaceId(int surface_id) {
+void SurfaceLayerImpl::SetSurfaceId(SurfaceId surface_id) {
   if (surface_id_ == surface_id)
     return;
 
   surface_id_ = surface_id;
   NoteLayerPropertyChanged();
 }
 
 void SurfaceLayerImpl::PushPropertiesTo(LayerImpl* layer) {
   LayerImpl::PushPropertiesTo(layer);
   SurfaceLayerImpl* layer_impl = static_cast<SurfaceLayerImpl*>(layer);
 
   layer_impl->SetSurfaceId(surface_id_);
 }
 
 void SurfaceLayerImpl::AppendQuads(QuadSink* quad_sink,
                                    AppendQuadsData* append_quads_data) {
   SharedQuadState* shared_quad_state = quad_sink->CreateSharedQuadState();
   PopulateSharedQuadState(shared_quad_state);
 
   AppendDebugBorderQuad(quad_sink, shared_quad_state, append_quads_data);
 
-  if (!surface_id_)
+  if (surface_id_.is_null())
     return;
 
   scoped_ptr<SurfaceDrawQuad> quad = SurfaceDrawQuad::Create();
   gfx::Rect quad_rect(content_bounds());
   gfx::Rect visible_quad_rect = quad_sink->UnoccludedContentRect(
       quad_rect, draw_properties().target_space_transform);
   if (visible_quad_rect.IsEmpty())
     return;
   quad->SetNew(shared_quad_state, quad_rect, visible_quad_rect, surface_id_);
   quad_sink->Append(quad.PassAs<DrawQuad>());
 }
 
 void SurfaceLayerImpl::GetDebugBorderProperties(SkColor* color,
                                                 float* width) const {
   *color = DebugColors::SurfaceLayerBorderColor();
   *width = DebugColors::SurfaceLayerBorderWidth(layer_tree_impl());
 }
 
 void SurfaceLayerImpl::AsValueInto(base::DictionaryValue* dict) const {
   LayerImpl::AsValueInto(dict);
-  dict->SetInteger("surface_id", surface_id_);
+  dict->SetInteger("surface_id", surface_id_.id);
 }
 
 const char* SurfaceLayerImpl::LayerTypeAsString() const {
   return "cc::SurfaceLayerImpl";
 }
 
 }  // namespace cc