Don't use identity as hash function for integers.

test/unittests/base/functional-unittest.cc

 // 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.
 
 #include "src/base/functional.h"
 
 #include <limits>
 #include <set>
 
 #include "test/unittests/test-utils.h"
@@ skipping 65 matching lines @@
   for (int i = 0; i < 128; ++i) {
     TypeParam v;
     this->rng()->NextBytes(&v, sizeof(v));
     EXPECT_EQ(h1(v), h2(v));
   }
 }
 
 
 TYPED_TEST(FunctionalTest, HashIsOkish) {
   const size_t kValues = 128;
-  const size_t kMinHashes = kValues / (sizeof(uint64_t) / sizeof(size_t));
+  const size_t kMinHashes = kValues / 4;
   std::set<TypeParam> vs;
   while (vs.size() != kValues) {
     TypeParam v;
     this->rng()->NextBytes(&v, sizeof(v));
     vs.insert(v);
   }
   std::set<size_t> hs;
   for (const auto& v : vs) {
     hash<TypeParam> h;
     hs.insert(h(v));
@@ skipping 25 matching lines @@
     TRACED_FOREACH(double, y, kDoubleValues) {
       hash<Foo> h;
       Foo foo = {x, y};
       EXPECT_EQ(hash_combine(x, y), h(foo));
     }
   }
 }
 
 }  // namespace base
 }  // namespace v8