Added |front|, |back|, |size|, |IsEmpty| to NewLinkedHashSet

Implemented |NewLinkedHashSet::front|, |NewLinkedHashSet::back|, |NewLinkedHashSet::size|, |NewLinkedHashSet::IsEmpty|.
Also added tests for those functions.
Along with this change, added DCHECK to |VectorBackedLinkedList::front| and |VectorBackedLinkedList::back|.

Change-Id: I8f90dd8b744b85dd4ceb8366a64398d5f88c34bb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2103595Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Reviewed-by: Bartek Nowierski <bartekn@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Kei Nakashima <keinakashima@google.com>
Cr-Commit-Position: refs/heads/master@{#750507}

third_party/blink/renderer/platform/wtf/linked_hash_set.h

@@ -1072,7 +1072,8 @@ class NewLinkedHashSet {
 
   void Swap(NewLinkedHashSet&);
 
-  // TODO(keinakashima): implement size-related functions
+  wtf_size_t size() const { return list_.size(); }
+  bool IsEmpty() const { return list_.empty(); }
 
   const_iterator begin() const { return list_.cbegin(); }
   const_iterator end() const { return list_.cend(); }
@@ -1080,7 +1081,8 @@ class NewLinkedHashSet {
   const_reverse_iterator rbegin() const { return list_.crbegin(); }
   const_reverse_iterator rend() const { return list_.crend(); }
 
-  // TODO(keinakashima): implement front/back
+  const Value& front() const { return list_.front(); }
+  const Value& back() const { return list_.back(); }
 
   const_iterator find(ValuePeekInType) const;
   bool Contains(ValuePeekInType) const;

third_party/blink/renderer/platform/wtf/linked_hash_set_test.cc

@@ -12,6 +12,8 @@ namespace WTF {
 
 TEST(NewLinkedHashSetTest, Construct) {
   NewLinkedHashSet<int> test;
+  EXPECT_EQ(test.size(), 0u);
+  EXPECT_TRUE(test.IsEmpty());
 }
 
 TEST(NewLinkedHashSetTest, Iterator) {
@@ -21,6 +23,33 @@ TEST(NewLinkedHashSetTest, Iterator) {
   EXPECT_TRUE(set.rbegin() == set.rend());
 }
 
+TEST(NewLinkedHashSetTest, FrontAndBack) {
+  using Set = NewLinkedHashSet<int>;
+  Set set;
+  EXPECT_EQ(set.size(), 0u);
+  EXPECT_TRUE(set.IsEmpty());
+
+  set.PrependOrMoveToFirst(1);
+  EXPECT_EQ(set.front(), 1);
+  EXPECT_EQ(set.back(), 1);
+
+  set.insert(2);
+  EXPECT_EQ(set.front(), 1);
+  EXPECT_EQ(set.back(), 2);
+
+  set.AppendOrMoveToLast(3);
+  EXPECT_EQ(set.front(), 1);
+  EXPECT_EQ(set.back(), 3);
+
+  set.PrependOrMoveToFirst(3);
+  EXPECT_EQ(set.front(), 3);
+  EXPECT_EQ(set.back(), 2);
+
+  set.AppendOrMoveToLast(1);
+  EXPECT_EQ(set.front(), 3);
+  EXPECT_EQ(set.back(), 1);
+}
+
 TEST(NewLinkedHashSetTest, Insert) {
   using Set = NewLinkedHashSet<int>;
   Set set;

third_party/blink/renderer/platform/wtf/vector_backed_linked_list.h

@@ -91,7 +91,7 @@ class VectorBackedLinkedList {
 
   void swap(VectorBackedLinkedList&);
 
-  bool empty() { return size_ == 0; }
+  bool empty() const { return size_ == 0; }
   wtf_size_t size() const { return size_; }
 
   iterator begin() { return MakeIterator(UsedFirstIndex()); }
@@ -107,10 +107,10 @@ class VectorBackedLinkedList {
     return MakeConstReverseIterator(anchor_index_);
   }
 
-  Value& front() { return nodes_[UsedFirstIndex()].value_; }
-  const Value& front() const { return nodes_[UsedFirstIndex()].value_; }
-  Value& back() { return nodes_[UsedLastIndex()].value_; }
-  const Value& back() const { return nodes_[UsedLastIndex()].value_; }
+  Value& front();
+  const Value& front() const;
+  Value& back();
+  const Value& back() const;
 
   template <typename IncomingValueType>
   iterator insert(const_iterator position, IncomingValueType&& value);
@@ -444,6 +444,30 @@ inline void VectorBackedLinkedList<T>::swap(VectorBackedLinkedList& other) {
 #endif
 }
 
+template <typename T>
+T& VectorBackedLinkedList<T>::front() {
+  DCHECK(!empty());
+  return nodes_[UsedFirstIndex()].value_;
+}
+
+template <typename T>
+const T& VectorBackedLinkedList<T>::front() const {
+  DCHECK(!empty());
+  return nodes_[UsedFirstIndex()].value_;
+}
+
+template <typename T>
+T& VectorBackedLinkedList<T>::back() {
+  DCHECK(!empty());
+  return nodes_[UsedLastIndex()].value_;
+}
+
+template <typename T>
+const T& VectorBackedLinkedList<T>::back() const {
+  DCHECK(!empty());
+  return nodes_[UsedLastIndex()].value_;
+}
+
 template <typename T>
 template <typename IncomingValueType>
 typename VectorBackedLinkedList<T>::iterator VectorBackedLinkedList<T>::insert(