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

cc/surfaces/surface_id.h

Index: cc/surfaces/surface_id.h
diff --git a/cc/surfaces/surface_id.h b/cc/surfaces/surface_id.h
index 070265a84955d3dee6b1ec29cea952268868e01c..fb58370852c6cb012a1f763332871da16d606b68 100644
--- a/cc/surfaces/surface_id.h
+++ b/cc/surfaces/surface_id.h
@@ -5,40 +5,13 @@
 #ifndef CC_SURFACES_SURFACE_ID_H_
 #define CC_SURFACES_SURFACE_ID_H_
 
-#include "base/containers/hash_tables.h"
+#include "base/id_type.h"
 
 namespace cc {
 
-struct SurfaceId {
-  SurfaceId() : id(0) {}
-  explicit SurfaceId(uint64_t id) : id(id) {}
-
-  bool is_null() const { return id == 0; }
-
-  uint64_t id;
-};
-
-inline bool operator==(const SurfaceId& a, const SurfaceId& b) {
-  return a.id == b.id;
-}
-
-inline bool operator!=(const SurfaceId& a, const SurfaceId& b) {
-  return !(a == b);
-}
-
-inline bool operator<(const SurfaceId& a, const SurfaceId& b) {
-  return a.id < b.id;
-}
+class Surface;
+using SurfaceId = base::IdType<Surface, uint64_t, 0>;
 
 }  // namespace cc
 
-namespace BASE_HASH_NAMESPACE {
-template <>
-struct hash<cc::SurfaceId> {
-  size_t operator()(cc::SurfaceId key) const {
-    return hash<uint64_t>()(key.id);
-  }
-};
-}  // namespace BASE_HASH_NAMESPACE
-
 #endif  // CC_SURFACES_SURFACE_ID_H_