Use a better hash function in IdentityMap.

src/identity-map.h

 // Copyright 2015 the V8 project 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 V8_IDENTITY_MAP_H_
 #define V8_IDENTITY_MAP_H_
 
+#include "src/base/functional.h"
 #include "src/handles.h"
 
 namespace v8 {
 namespace internal {
 
 // Forward declarations.
 class Heap;
 class Zone;
 
 // Base class of identity maps contains shared code for all template
@@ skipping 23 matching lines @@
  private:
   // Internal implementation should not be called directly by subclasses.
   int LookupIndex(Object* address);
   int InsertIndex(Object* address);
   void Rehash();
   void Resize();
   RawEntry Lookup(Object* key);
   RawEntry Insert(Object* key);
   int Hash(Object* address);
 
+  base::hash<uintptr_t> hasher_;
   Heap* heap_;
   Zone* zone_;
   int gc_counter_;
   int size_;
   int mask_;
   Object** keys_;
   void** values_;
 };
 
 // Implements an identity map from object addresses to a given value type {V}.
@@ skipping 26 matching lines @@
   void Set(Handle<Object> key, V v) { Set(*key, v); }
   void Set(Object* key, V v) { *(reinterpret_cast<V*>(GetEntry(key))) = v; }
 
   // Removes all elements from the map.
   void Clear() { IdentityMapBase::Clear(); }
 };
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_IDENTITY_MAP_H_