WIP for display item list backed by ListContainer

Source/platform/graphics/paint/DisplayItemList.cpp

Index: Source/platform/graphics/paint/DisplayItemList.cpp
diff --git a/Source/platform/graphics/paint/DisplayItemList.cpp b/Source/platform/graphics/paint/DisplayItemList.cpp
index d4762fa9b765cad05b8f4b92f192bd44d2caf3e9..a51c90a07369bf0cfa689f34c85e8a03d1c8f7e1 100644
--- a/Source/platform/graphics/paint/DisplayItemList.cpp
+++ b/Source/platform/graphics/paint/DisplayItemList.cpp
@@ -60,7 +60,7 @@ void DisplayItemList::removeLastDisplayItem()
     m_newDisplayItems.removeLast();
 }
 
-void DisplayItemList::add(WTF::PassOwnPtr<DisplayItem> displayItem)
+void DisplayItemList::processNewItem(DisplayItem* displayItem)
 {
     ASSERT(RuntimeEnabledFeatures::slimmingPaintEnabled());
     ASSERT(!m_constructionDisabled);
@@ -70,9 +70,10 @@ void DisplayItemList::add(WTF::PassOwnPtr<DisplayItem> displayItem)
         ++m_numCachedItems;
 
 #if ENABLE(ASSERT)
-    // Verify noop begin/end pairs have been removed.
-    if (!m_newDisplayItems.isEmpty() && m_newDisplayItems.last().isBegin() && !m_newDisplayItems.last().drawsContent())
-        ASSERT(!displayItem->isEndAndPairedWith(m_newDisplayItems.last().type()));
+// TODO(pdr): Reenable this assert. Note that the item has already been appended.
+//    // Verify noop begin/end pairs have been removed.
+//    if (!m_newDisplayItems.isEmpty() && m_newDisplayItems.last().isBegin() && !m_newDisplayItems.last().drawsContent())
+//        ASSERT(!displayItem->isEndAndPairedWith(m_newDisplayItems.last().type()));
 #endif
 
     if (!m_scopeStack.isEmpty())
@@ -88,14 +89,12 @@ void DisplayItemList::add(WTF::PassOwnPtr<DisplayItem> displayItem)
 #endif
         ASSERT_NOT_REACHED();
     }
-    addItemToIndex(displayItem->client(), displayItem->type(), m_newDisplayItems.size(), m_newDisplayItemIndicesByClient);
+    addItemToIndex(displayItem->client(), displayItem->type(), m_newDisplayItems.size() - 1, m_newDisplayItemIndicesByClient);
 #endif // ENABLE(ASSERT)
 
     ASSERT(!displayItem->skippedCache()); // Only DisplayItemList can set the flag.
     if (skippingCache())
         displayItem->setSkippedCache();
-
-    m_newDisplayItems.append(displayItem);
 }
 
 void DisplayItemList::beginScope(DisplayItemClient client)
@@ -263,7 +262,8 @@ void DisplayItemList::commitNewDisplayItems()
     }
 #endif // ENABLE(ASSERT)
 
-    DisplayItems updatedList;
+    // TODO(pdr): Use some smarts to set this initial capacity.
+    DisplayItems updatedList(kInitialDisplayItemsCapacity);
     DisplayItems::Iterator currentIt = m_currentDisplayItems.begin();
     DisplayItems::Iterator currentEnd = m_currentDisplayItems.end();
     for (DisplayItems::Iterator newIt = m_newDisplayItems.begin(); newIt != m_newDisplayItems.end(); ++newIt) {