Allow WTF::Vector::emplace_back accept one or zero arguments

third_party/WebKit/Source/wtf/VectorTest.cpp

 /*
  * Copyright (C) 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 656 matching lines @@
 TEST(VectorTest, Optional) {
   Optional<Vector<int>> vector;
   EXPECT_FALSE(vector);
   vector.emplace(3);
   EXPECT_TRUE(vector);
   EXPECT_EQ(3u, vector->size());
 }
 
 TEST(VectorTest, emplace_back) {
   struct Item {
+    Item() = default;
+    explicit Item(int value1) : value1(value1), value2() {}
     Item(int value1, int value2) : value1(value1), value2(value2) {}
     int value1;
     int value2;
   };
 
   Vector<Item> vector;
   vector.emplace_back(1, 2);
   vector.emplace_back(3, 4);
+  vector.emplace_back(5);
+  vector.emplace_back();
 
-  EXPECT_EQ(2u, vector.size());
+  EXPECT_EQ(4u, vector.size());
+
   EXPECT_EQ(1, vector[0].value1);
   EXPECT_EQ(2, vector[0].value2);
+
   EXPECT_EQ(3, vector[1].value1);
   EXPECT_EQ(4, vector[1].value2);
+
+  EXPECT_EQ(5, vector[2].value1);
+  EXPECT_EQ(0, vector[2].value2);
+
+  EXPECT_EQ(0, vector[3].value1);
+  EXPECT_EQ(0, vector[3].value2);
+
+  // Test returned value.
+  Item& item = vector.emplace_back(6, 7);
+  EXPECT_EQ(6, item.value1);
+  EXPECT_EQ(7, item.value2);
 }
 
 static_assert(VectorTraits<int>::canCopyWithMemcpy,
               "int should be copied with memcopy.");
 static_assert(VectorTraits<char>::canCopyWithMemcpy,
               "char should be copied with memcpy.");
 static_assert(VectorTraits<LChar>::canCopyWithMemcpy,
               "LChar should be copied with memcpy.");
 static_assert(VectorTraits<UChar>::canCopyWithMemcpy,
               "UChar should be copied with memcpy.");
 
 class UnknownType;
 static_assert(VectorTraits<UnknownType*>::canCopyWithMemcpy,
               "Pointers should be copied with memcpy.");
 
 }  // anonymous namespace
 
 }  // namespace WTF