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

cc/layers/surface_layer_impl_unittest.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/test/layer_test_common.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace cc {
 namespace {
 
 TEST(SurfaceLayerImplTest, Occlusion) {
   gfx::Size layer_size(1000, 1000);
   gfx::Size viewport_size(1000, 1000);
 
   LayerTestCommon::LayerImplTest impl;
 
   SurfaceLayerImpl* surface_layer_impl =
       impl.AddChildToRoot<SurfaceLayerImpl>();
   surface_layer_impl->SetBounds(layer_size);
   surface_layer_impl->SetContentBounds(layer_size);
   surface_layer_impl->SetDrawsContent(true);
-  surface_layer_impl->SetSurfaceId(9);
+  SurfaceId surface_id;
+  surface_id.id = 9;

[piman, 2014/06/11 23:48:59]

nit: add an explicit constructor?

+  surface_layer_impl->SetSurfaceId(surface_id);
 
   impl.CalcDrawProps(viewport_size);
 
   {
     SCOPED_TRACE("No occlusion");
     gfx::Rect occluded;
     impl.AppendQuadsWithOcclusion(surface_layer_impl, occluded);
 
     LayerTestCommon::VerifyQuadsExactlyCoverRect(impl.quad_list(),
                                                  gfx::Rect(layer_size));
@@ skipping 21 matching lines @@
         occluded,
         &partially_occluded_count);
     // The layer outputs one quad, which is partially occluded.
     EXPECT_EQ(1u, impl.quad_list().size());
     EXPECT_EQ(1u, partially_occluded_count);
   }
 }
 
 }  // namespace
 }  // namespace cc