Don't use identity as hash function for integers.

src/base/functional.h

 // Copyright 2014 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_BASE_FUNCTIONAL_H_
 #define V8_BASE_FUNCTIONAL_H_
 
 #include <cstddef>
 #include <functional>
 #include <utility>
@@ skipping 58 matching lines @@
 inline size_t hash_combine(T const& v, Ts const&... vs) {
   return hash_combine(hash<T>()(v), hash_combine(vs...));
 }
 
 
 #define V8_BASE_HASH_VALUE_TRIVIAL(type) \
   inline size_t hash_value(type v) { return static_cast<size_t>(v); }
 V8_BASE_HASH_VALUE_TRIVIAL(bool)
 V8_BASE_HASH_VALUE_TRIVIAL(unsigned char)
 V8_BASE_HASH_VALUE_TRIVIAL(unsigned short)  // NOLINT(runtime/int)
-V8_BASE_HASH_VALUE_TRIVIAL(unsigned int)
 #undef V8_BASE_HASH_VALUE_TRIVIAL
 
-size_t hash_value(unsigned long v);       // NOLINT(runtime/int)
-size_t hash_value(unsigned long long v);  // NOLINT(runtime/int)
+size_t hash_value(unsigned int);
+size_t hash_value(unsigned long);       // NOLINT(runtime/int)
+size_t hash_value(unsigned long long);  // NOLINT(runtime/int)
 
 #define V8_BASE_HASH_VALUE_SIGNED(type)            \
   inline size_t hash_value(signed type v) {        \
     return hash_value(bit_cast<unsigned type>(v)); \
   }
 V8_BASE_HASH_VALUE_SIGNED(char)
 V8_BASE_HASH_VALUE_SIGNED(short)      // NOLINT(runtime/int)
 V8_BASE_HASH_VALUE_SIGNED(int)        // NOLINT(runtime/int)
 V8_BASE_HASH_VALUE_SIGNED(long)       // NOLINT(runtime/int)
 V8_BASE_HASH_VALUE_SIGNED(long long)  // NOLINT(runtime/int)
@@ skipping 51 matching lines @@
     : public std::unary_function<std::pair<T1, T2>, size_t> {
   size_t operator()(std::pair<T1, T2> const& v) const {
     return ::v8::base::hash_value(v);
   }
 };
 
 }  // namespace base
 }  // namespace v8
 
 #endif  // V8_BASE_FUNCTIONAL_H_