Reusing base::IdType<...> to implement SurfaceId.

cc/surfaces/surface_hittest_unittest.cc

 // Copyright 2015 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 <stddef.h>
 
 #include "cc/output/compositor_frame.h"
 #include "cc/surfaces/surface.h"
 #include "cc/surfaces/surface_factory.h"
 #include "cc/surfaces/surface_factory_client.h"
@@ skipping 53 matching lines @@
   SurfaceFactory factory(&manager, &client);
 
   // Creates a root surface.
   gfx::Rect root_rect(300, 300);
   RenderPass* root_pass = nullptr;
   scoped_ptr<CompositorFrame> root_frame =
       CreateCompositorFrame(root_rect, &root_pass);
 
   // Add a reference to a non-existant child surface on the root surface.
   SurfaceIdAllocator child_allocator(3);
-  SurfaceId child_surface_id;
-  child_surface_id.id = 0xdeadbeef;
+  SurfaceId child_surface_id = SurfaceId::FromUnsafeValue(0xdeadbeef);
   gfx::Rect child_rect(200, 200);
   CreateSurfaceDrawQuad(root_pass,
                         gfx::Transform(),
                         root_rect,
                         child_rect,
                         child_surface_id);
 
   // Submit the root frame.
   SurfaceIdAllocator root_allocator(2);
   SurfaceId root_surface_id = root_allocator.GenerateId();
@@ skipping 501 matching lines @@
   RunTests(&delegate, &manager, test_expectations_with_insets,
            arraysize(test_expectations_with_insets));
 
   // Verify that insets have affected hit targeting.
   EXPECT_EQ(2, delegate.target_overrides());
 
   factory.Destroy(root_surface_id);
 }
 
 }  // namespace cc