Added iterators to NewLinkedHashSet

Implemented iterators of NewLinkedHashSet using those of VectorBackedLinkedList.
Also made some iterator-related APIs public to use them in NewLinkedHashSet.

Change-Id: Ifa4a7c60bfbd3673a1f3923f911cde3eebca612f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2097904
Commit-Queue: Kei Nakashima <keinakashima@google.com>
Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#749587}

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

@@ -1045,6 +1045,10 @@ class NewLinkedHashSet {
   using Map = HashMap<Value, wtf_size_t>;
 
  public:
+  using const_iterator = typename VectorBackedLinkedList<Value>::const_iterator;
+  using const_reverse_iterator =
+      typename VectorBackedLinkedList<Value>::const_reverse_iterator;
+
   // TODO(keinakashima): add security check
   struct AddResult final {
     STACK_ALLOCATED();
@@ -1070,7 +1074,11 @@ class NewLinkedHashSet {
 
   // TODO(keinakashima): implement size-related functions
 
-  // TODO(keinakashima): implement begin/end, rbegin/rend
+  const_iterator begin() const { return list_.cbegin(); }
+  const_iterator end() const { return list_.cend(); }
+
+  const_reverse_iterator rbegin() const { return list_.crbegin(); }
+  const_reverse_iterator rend() const { return list_.crend(); }
 
   // TODO(keinakashima): implement front/back
 

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

@@ -14,4 +14,11 @@ TEST(NewLinkedHashSetTest, Construct) {
   NewLinkedHashSet<int> test;
 }
 
+TEST(NewLinkedHashSetTest, Iterator) {
+  using Set = NewLinkedHashSet<int>;
+  Set set;
+  EXPECT_TRUE(set.begin() == set.end());
+  EXPECT_TRUE(set.rbegin() == set.rend());
+}
+
 }  // namespace WTF

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

@@ -182,6 +182,9 @@ class VectorBackedLinkedList {
   // terminator.
   wtf_size_t free_head_index_ = anchor_index_;
   wtf_size_t size_ = 0;
+
+  template <typename T>
+  friend class NewLinkedHashSet;
 };
 
 template <typename VectorBackedLinkedListType>
@@ -241,9 +244,18 @@ class VectorBackedLinkedListConstIterator {
   using Node = typename VectorBackedLinkedListType::Node;
 
  public:
+  PointerType Get() const {
+    DCHECK(container_->IsIndexValid(index_));
+    DCHECK(!container_->IsAnchor(index_));
+    const Node& node = container_->nodes_[index_];
+    return &node.value_;
+  }
+
   ReferenceType operator*() const { return *Get(); }
   PointerType operator->() const { return Get(); }
 
+  wtf_size_t GetIndex() const { return index_; }
+
   VectorBackedLinkedListConstIterator& operator++() {
     DCHECK(container_->IsIndexValid(index_));
     index_ = container_->nodes_[index_].next_index_;
@@ -271,19 +283,12 @@ class VectorBackedLinkedListConstIterator {
   }
 
  protected:
-  PointerType Get() const {
-    DCHECK(container_->IsIndexValid(index_));
-    DCHECK(!container_->IsAnchor(index_));
-    const Node& node = container_->nodes_[index_];
-    return &node.value_;
-  }
-
   VectorBackedLinkedListConstIterator(
       wtf_size_t index,
       const VectorBackedLinkedListType* container)
-      : index_(index), container_(container) {}
-
-  wtf_size_t GetIndex() const { return index_; }
+      : index_(index), container_(container) {
+    DCHECK(container_->IsIndexValid(index_));
+  }
 
  private:
   wtf_size_t index_;