WIP for display item list backed by ListContainer

Source/platform/graphics/paint/DisplayItems.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "platform/graphics/paint/DisplayItems.h"
 
 namespace blink {
 
-DisplayItems::DisplayItems()
-{
-}
-
 DisplayItems::~DisplayItems()
 {
 }
 
-void DisplayItems::append(PassOwnPtr<DisplayItem> displayItem)
+void DisplayItems::appendByMoving(const Iterator& other)
 {
-    m_items.append(displayItem);
-}
-
-void DisplayItems::appendByMoving(const Iterator& it)
-{
-    // Release the underlying OwnPtr to move the display item ownership.
-    ASSERT(!it->isGone());
-    append(it.m_iterator->release());
+    ASSERT(!other->isGone());
+    size_t indexInSource = other.m_iterator - other.m_owningList->m_ptrs.begin();
+    DisplayItem* source = other.m_owningList->m_ptrs[indexInSource];
+    m_items.appendByMoving(source);
+    m_ptrs.append(source);
+    other.m_owningList->m_ptrs[indexInSource] = nullptr;
 }
 
 void DisplayItems::removeLast()
 {
+    m_ptrs.removeLast();
     m_items.removeLast();
 }
 
 void DisplayItems::clear()
 {
+    m_ptrs.clear();
     m_items.clear();
 }
 
 void DisplayItems::swap(DisplayItems& other)
 {
+    m_ptrs.swap(other.m_ptrs);
     m_items.swap(other.m_items);
 }
 
 void DisplayItems::setGone(const Iterator& it)
 {
-    it.m_iterator->clear();
+    size_t index = it.m_iterator - it.m_owningList->m_ptrs.begin();
+    m_ptrs[index] = nullptr;
 }
 
 } // namespace blink