WIP for display item list backed by ListContainer

Source/platform/graphics/paint/DisplayItemList.h

 // Copyright 2014 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.
 
 #ifndef DisplayItemList_h
 #define DisplayItemList_h
 
 #include "platform/PlatformExport.h"
 #include "platform/graphics/paint/DisplayItem.h"
 #include "platform/graphics/paint/DisplayItems.h"
 #include "wtf/HashMap.h"
 #include "wtf/PassOwnPtr.h"
 #include "wtf/Vector.h"
 
 namespace blink {
 
 class GraphicsContext;
 
+static const size_t kInitialDisplayItemsCapacity = 32;
+
 class PLATFORM_EXPORT DisplayItemList {
     WTF_MAKE_NONCOPYABLE(DisplayItemList);
     WTF_MAKE_FAST_ALLOCATED(DisplayItemList);
 public:
     static PassOwnPtr<DisplayItemList> create()
     {
         return adoptPtr(new DisplayItemList());
     }
 
     // These methods are called during paint invalidation.
     void invalidate(DisplayItemClient);
     void invalidateAll();
 
     // These methods are called during painting.
-    void add(WTF::PassOwnPtr<DisplayItem>);
+    template<typename DisplayItemClass>
+    DisplayItemClass& createAndAppend(const DisplayItemClientWrapper& client, DisplayItem::Type type)
+    {
+        DisplayItemClass& item = m_newDisplayItems.createAndAppend<DisplayItemClass>();
+        item.setClientAndType(client, type);
+        processNewItem(&item);
+        return item;
+    }
+    void add(WTF::PassOwnPtr<DisplayItem>) { } // REMOVE ME
     void beginScope(DisplayItemClient);
     void endScope(DisplayItemClient);
 
     // True if the last display item is a begin that doesn't draw content.
     bool lastDisplayItemIsNoopBegin() const;
     void removeLastDisplayItem();
 
     void beginSkippingCache() { ++m_skippingCacheCount; }
     void endSkippingCache() { ASSERT(m_skippingCacheCount > 0); --m_skippingCacheCount; }
     bool skippingCache() const { return m_skippingCacheCount; }
@@ skipping 21 matching lines @@
 #if ENABLE(ASSERT)
     size_t newDisplayItemsSize() const { return m_newDisplayItems.size(); }
 #endif
 
 #ifndef NDEBUG
     void showDebugData() const;
 #endif
 
 protected:
     DisplayItemList()
-        : m_validlyCachedClientsDirty(false)
+        : m_currentDisplayItems(kInitialDisplayItemsCapacity)
+        , m_newDisplayItems(kInitialDisplayItemsCapacity)
+        , m_validlyCachedClientsDirty(false)
         , m_constructionDisabled(false)
         , m_skippingCacheCount(0)
         , m_numCachedItems(0) { }
 
 private:
     friend class DisplayItemListTest;
     friend class DisplayItemListPaintTest;
     friend class LayoutObjectDrawingRecorderTest;
 
+    // Set new item state (scopes, cache skipping, etc) for a new item.
+    // TODO(pdr): This only passes a pointer to make the patch easier to review. Change to a reference.
+    void processNewItem(DisplayItem*);
+
     void updateValidlyCachedClientsIfNeeded() const;
 
 #ifndef NDEBUG
     WTF::String displayItemsAsDebugString(const DisplayItems&) const;
 #endif
 
     // Indices into PaintList of all DrawingDisplayItems and BeginSubtreeDisplayItems of each client.
     // Temporarily used during merge to find out-of-order display items.
     using DisplayItemIndicesByClientMap = HashMap<DisplayItemClient, Vector<size_t>>;
 
@@ skipping 45 matching lines @@
     // This is used to check duplicated ids during add(). We could also check during
     // updatePaintList(), but checking during add() helps developer easily find where
     // the duplicated ids are from.
     DisplayItemIndicesByClientMap m_newDisplayItemIndicesByClient;
 #endif
 };
 
 } // namespace blink
 
 #endif // DisplayItemList_h