Switch SurfaceId maps from base::hash_map to std::unordered_map.

cc/surfaces/surface_id.h

 // 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.
 
 #ifndef CC_SURFACES_SURFACE_ID_H_
 #define CC_SURFACES_SURFACE_ID_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 23 matching lines @@
 }
 
 struct SurfaceIdHash {
   size_t operator()(const SurfaceId& key) const {
     return std::hash<uint64_t>()(key.id);
   }
 };
 
 }  // 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_