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

content/browser/renderer_host/render_widget_host_input_event_router.h

Index: content/browser/renderer_host/render_widget_host_input_event_router.h
diff --git a/content/browser/renderer_host/render_widget_host_input_event_router.h b/content/browser/renderer_host/render_widget_host_input_event_router.h
index ec45f1543c9be9d5d9d044c91c19b1c24a7326ff..b7cc76e042f62f3c7c591c3e687e2bbb105c8289 100644
--- a/content/browser/renderer_host/render_widget_host_input_event_router.h
+++ b/content/browser/renderer_host/render_widget_host_input_event_router.h
@@ -71,12 +71,13 @@ class CONTENT_EXPORT RenderWidgetHostInputEventRouter {
   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_;
   };
 
@@ -91,7 +92,7 @@ class CONTENT_EXPORT RenderWidgetHostInputEventRouter {
   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);