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

content/browser/renderer_host/render_widget_host_input_event_router.h

 // 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.
 
 #ifndef CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_INPUT_EVENT_ROUTER_H_
 #define CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_INPUT_EVENT_ROUTER_H_
 
 #include <stdint.h>
 #include <unordered_map>
 
@@ skipping 53 matching lines @@
   void OnHittestData(const FrameHostMsg_HittestData_Params& params);
 
  private:
   struct HittestData {
     bool ignored_for_hittest;
   };
 
   class HittestDelegate : public cc::SurfaceHittestDelegate {
    public:
     HittestDelegate(
-        const std::unordered_map<cc::SurfaceId, HittestData, cc::SurfaceIdHash>&
-            hittest_data);
+        const std::unordered_map<cc::SurfaceId,
+                                 HittestData,
+                                 cc::SurfaceId::Hasher>& hittest_data);
     bool RejectHitTarget(const cc::SurfaceDrawQuad* surface_quad,
                          const gfx::Point& point_in_quad_space) override;
 
-    const std::unordered_map<cc::SurfaceId, HittestData, cc::SurfaceIdHash>&
+    const std::unordered_map<cc::SurfaceId, HittestData, cc::SurfaceId::Hasher>&
         hittest_data_;
   };
 
   using WeakTarget = base::WeakPtr<RenderWidgetHostViewBase>;
   using SurfaceIdNamespaceOwnerMap =
       base::hash_map<uint32_t, base::WeakPtr<RenderWidgetHostViewBase>>;
 
   RenderWidgetHostViewBase* FindEventTarget(RenderWidgetHostViewBase* root_view,
                                             const gfx::Point& point,
                                             gfx::Point* transformed_point);
 
   SurfaceIdNamespaceOwnerMap owner_map_;
   WeakTarget current_touch_target_;
   int active_touches_;
-  std::unordered_map<cc::SurfaceId, HittestData, cc::SurfaceIdHash>
+  std::unordered_map<cc::SurfaceId, HittestData, cc::SurfaceId::Hasher>
       hittest_data_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderWidgetHostInputEventRouter);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_INPUT_EVENT_ROUTER_H_