Fixed bugs in VectorBackedLinkedList::MoveTo

|MoveTo| didn't work correctly when moving the target node before itself/its next node.
Also added DCHECKs, which check if the target node is not anchor and if two given node is both in-use list.

Change-Id: I60442f1d706a072eaeca9bc83eaaee9d60b0c853
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2096316
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@{#748599}

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

@@ -432,14 +432,23 @@ typename VectorBackedLinkedList<T>::iterator VectorBackedLinkedList<T>::insert(
 template <typename T>
 void VectorBackedLinkedList<T>::MoveTo(const_iterator target,
                                        const_iterator new_position) {
+  DCHECK(target != end());
+  if (target == new_position)
+    return;
+
   wtf_size_t target_index = target.GetIndex();
   Node& target_node = nodes_[target_index];
+  wtf_size_t new_position_index = new_position.GetIndex();
+  Node& new_position_node = nodes_[new_position_index];
+  wtf_size_t prev_index = new_position_node.prev_index_;
+
+  if (prev_index == target_index)
+    return;
+
   Unlink(target_node);
 
-  wtf_size_t new_position_index = new_position.GetIndex();
-  wtf_size_t prev_index = nodes_[new_position_index].prev_index_;
   nodes_[prev_index].next_index_ = target_index;
-  nodes_[new_position_index].prev_index_ = target_index;
+  new_position_node.prev_index_ = target_index;
   target_node.prev_index_ = prev_index;
   target_node.next_index_ = new_position_index;
 }
@@ -456,6 +465,7 @@ typename VectorBackedLinkedList<T>::iterator VectorBackedLinkedList<T>::erase(
   node.value_ = HashTraits<T>::EmptyValue();
 
   node.next_index_ = free_head_index_;
+  node.prev_index_ = kNotFound;
   free_head_index_ = position_index;
 
   size_--;

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

@@ -77,13 +77,16 @@ TEST(VectorBackedLinkedList, MoveTo) {
   List list;
 
   list.push_back(1);
+  list.MoveTo(list.begin(), list.end());
+  List::iterator it = list.begin();
+  EXPECT_EQ(*it, 1);
   list.push_back(2);
   list.push_back(3);
 
   List::iterator target = list.begin();
   list.MoveTo(target, list.end());  // {2, 3, 1}
 
-  List::iterator it = list.begin();
+  it = list.begin();
   EXPECT_EQ(*it, 2);
   ++it;
   EXPECT_EQ(*it, 3);
@@ -108,6 +111,24 @@ TEST(VectorBackedLinkedList, MoveTo) {
   EXPECT_EQ(*it, 1);
   ++it;
   EXPECT_EQ(*it, 2);
+
+  list.MoveTo(list.begin(), list.begin());
+  it = list.begin();
+  EXPECT_EQ(*it, 3);
+  ++it;
+  EXPECT_EQ(*it, 1);
+  ++it;
+  EXPECT_EQ(*it, 2);
+
+  target = list.begin();
+  List::iterator position = ++list.begin();
+  list.MoveTo(target, position);
+  it = list.begin();
+  EXPECT_EQ(*it, 3);
+  ++it;
+  EXPECT_EQ(*it, 1);
+  ++it;
+  EXPECT_EQ(*it, 2);
 }
 
 TEST(VectorBackedLinkedList, Erase) {