Fix wtf::PairHashTraits to support types with isEmptyValue.

Types such as RefPtr<P> provide a custom isEmptyValue function in their
HashTraits. This fixes the std::pair HashTraits to support using such
types in a std::pair.

Review-Url: https://codereview.chromium.org/2042453002
Cr-Commit-Position: refs/heads/master@{#397861}

third_party/WebKit/Source/wtf/HashMapTest.cpp

@@ -608,6 +608,67 @@ TEST(HashMapTest, UniquePtrAsValue)
     }
 }
 
+TEST(HashMapTest, MoveOnlyPairKeyType)
+{
+    using Pair = std::pair<MoveOnly, int>;
+    using TheMap = HashMap<Pair, int>;
+    TheMap map;
+    {
+        TheMap::AddResult addResult = map.add(Pair(MoveOnly(1), -1), 10);
+        EXPECT_TRUE(addResult.isNewEntry);
+        EXPECT_EQ(1, addResult.storedValue->key.first.value());
+        EXPECT_EQ(-1, addResult.storedValue->key.second);
+        EXPECT_EQ(10, addResult.storedValue->value);
+    }
+    auto iter = map.find(Pair(MoveOnly(1), -1));
+    ASSERT_TRUE(iter != map.end());
+    EXPECT_EQ(1, iter->key.first.value());
+    EXPECT_EQ(-1, iter->key.second);
+    EXPECT_EQ(10, iter->value);
+
+    iter = map.find(Pair(MoveOnly(1), 0));
+    EXPECT_TRUE(iter == map.end());
+
+    for (int i = 2; i < 32; ++i) {
+        TheMap::AddResult addResult = map.add(Pair(MoveOnly(i), -i), i * 10);
+        EXPECT_TRUE(addResult.isNewEntry);
+        EXPECT_EQ(i, addResult.storedValue->key.first.value());
+        EXPECT_EQ(-i, addResult.storedValue->key.second);
+        EXPECT_EQ(i * 10, addResult.storedValue->value);
+    }
+
+    iter = map.find(Pair(MoveOnly(1), -1));
+    ASSERT_TRUE(iter != map.end());
+    EXPECT_EQ(1, iter->key.first.value());
+    EXPECT_EQ(-1, iter->key.second);
+    EXPECT_EQ(10, iter->value);
+
+    iter = map.find(Pair(MoveOnly(7), -7));
+    ASSERT_TRUE(iter != map.end());
+    EXPECT_EQ(7, iter->key.first.value());
+    EXPECT_EQ(-7, iter->key.second);
+    EXPECT_EQ(70, iter->value);
+
+    {
+        TheMap::AddResult addResult = map.set(Pair(MoveOnly(9), -9), 999);
+        EXPECT_FALSE(addResult.isNewEntry);
+        EXPECT_EQ(9, addResult.storedValue->key.first.value());
+        EXPECT_EQ(-9, addResult.storedValue->key.second);
+        EXPECT_EQ(999, addResult.storedValue->value);
+    }
+
+    map.remove(Pair(MoveOnly(11), -11));
+    iter = map.find(Pair(MoveOnly(11), -11));
+    EXPECT_TRUE(iter == map.end());
+
+    int oneThirty = map.take(Pair(MoveOnly(13), -13));
+    EXPECT_EQ(130, oneThirty);
+    iter = map.find(Pair(MoveOnly(13), -13));
+    EXPECT_TRUE(iter == map.end());
+
+    map.clear();
+}
+
 } // anonymous namespace
 
 } // namespace WTF

third_party/WebKit/Source/wtf/HashTraits.h

@@ -245,6 +245,9 @@ struct PairHashTraits : GenericHashTraits<std::pair<typename FirstTraitsArg::Tra
     static const bool emptyValueIsZero = FirstTraits::emptyValueIsZero && SecondTraits::emptyValueIsZero;
     static EmptyValueType emptyValue() { return std::make_pair(FirstTraits::emptyValue(), SecondTraits::emptyValue()); }
 
+    static const bool hasIsEmptyValueFunction = FirstTraits::hasIsEmptyValueFunction || SecondTraits::hasIsEmptyValueFunction;
+    static bool isEmptyValue(const TraitType& value) { return isHashTraitsEmptyValue<FirstTraits>(value.first) && isHashTraitsEmptyValue<SecondTraits>(value.second); }
+
     static const unsigned minimumTableSize = FirstTraits::minimumTableSize;
 
     static void constructDeletedValue(TraitType& slot, bool zeroValue)