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

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"
@@ skipping 12 matching lines @@
     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>);
+
+    // Moves from the provided display item for efficiency.
+    // (i.e. some values, like DrawingDisplayItem's picture, may be null)
+    void add(DisplayItem&);
+
     void beginScope(DisplayItemClient);
     void endScope(DisplayItemClient);
 
     void beginSkippingCache() { ++m_skippingCacheCount; }
     void endSkippingCache() { ASSERT(m_skippingCacheCount > 0); --m_skippingCacheCount; }
     bool skippingCache() const { return m_skippingCacheCount; }
 
     // Must be called when a painting is finished.
     void commitNewDisplayItems();
 
@@ skipping 89 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