[Slimming Paint] Blink-side contiguous allocation of display items.

Source/platform/graphics/paint/CachedDisplayItem.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 CachedDisplayItem_h
 #define CachedDisplayItem_h
 
 #include "platform/graphics/paint/DisplayItem.h"
 #include "wtf/Assertions.h"
 
 namespace blink {
 
 // A placeholder of DisplayItem in the new paint list of DisplayItemList, to indicate that
 // the DisplayItem has not been changed and should be replaced with the cached DisplayItem
 // when merging new paint list to cached paint list.
 class PLATFORM_EXPORT CachedDisplayItem : public DisplayItem {
     WTF_MAKE_FAST_ALLOCATED(CachedDisplayItem);
 public:
     static PassOwnPtr<CachedDisplayItem> create(const DisplayItemClientWrapper& client, Type type)
     {
         return adoptPtr(new CachedDisplayItem(client, type));
     }
 
-private:
     CachedDisplayItem(const DisplayItemClientWrapper& client, Type type)
         : DisplayItem(client, type)
     {
         ASSERT(isCachedType(type));
     }
 
+private:
     // CachedDisplayItem is never replayed or appended to WebDisplayItemList.
     virtual void replay(GraphicsContext&) override final { ASSERT_NOT_REACHED(); }
     virtual void appendToWebDisplayItemList(WebDisplayItemList*) const override final { ASSERT_NOT_REACHED(); }
+
+    virtual void appendByMoving(DisplayItems&) override;
 };
 
 } // namespace blink
 
 #endif // CachedDisplayItem_h