WIP for display item list backed by ListContainer

Source/platform/graphics/paint/DisplayItems.cpp

Index: Source/platform/graphics/paint/DisplayItems.cpp
diff --git a/Source/platform/graphics/paint/DisplayItems.cpp b/Source/platform/graphics/paint/DisplayItems.cpp
index 78c940dd9fbb388db8aafa2f38485e799f974a76..26aba57f1b8331b5450dc217b960da99a080012e 100644
--- a/Source/platform/graphics/paint/DisplayItems.cpp
+++ b/Source/platform/graphics/paint/DisplayItems.cpp
@@ -7,44 +7,42 @@
 
 namespace blink {
 
-DisplayItems::DisplayItems()
-{
-}
-
 DisplayItems::~DisplayItems()
 {
 }
 
-void DisplayItems::append(PassOwnPtr<DisplayItem> displayItem)
-{
-    m_items.append(displayItem);
-}
-
-void DisplayItems::appendByMoving(const Iterator& it)
+void DisplayItems::appendByMoving(const Iterator& other)
 {
-    // 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