Move use of DisplayItemList's vector behind an explicit DisplayItems interface.

Source/platform/graphics/ContentLayerDelegate.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *     notice, this list of conditions and the following disclaimer in the
@@ skipping 72 matching lines @@
         displayItemList->invalidateAll();
 
     GraphicsContext::DisabledMode disabledMode = GraphicsContext::NothingDisabled;
     if (paintingControl == WebContentLayerClient::DisplayListPaintingDisabled
         || paintingControl == WebContentLayerClient::DisplayListConstructionDisabled)
         disabledMode = GraphicsContext::FullyDisabled;
     GraphicsContext context(displayItemList, disabledMode);
 
     m_painter->paint(context, clip);
 
-    displayItemList->commitNewDisplayItems();
-
-    const DisplayItems& paintList = displayItemList->displayItems();
-    for (DisplayItems::const_iterator it = paintList.begin(); it != paintList.end(); ++it)
-        (*it)->appendToWebDisplayItemList(webDisplayItemList);
+    displayItemList->commitNewDisplayItemsAndAppendToWebDisplayItemList(webDisplayItemList);
 }
 
 } // namespace blink