Blink-side contiguous allocation of display items.

Source/platform/graphics/paint/DisplayItemList.h

Index: Source/platform/graphics/paint/DisplayItemList.h
diff --git a/Source/platform/graphics/paint/DisplayItemList.h b/Source/platform/graphics/paint/DisplayItemList.h
index 51dc0f8289d6a6b88eccc3d471a86f9de37706bb..ab039d9c888e94f7552f9f2312ba9b70280dea86 100644
--- a/Source/platform/graphics/paint/DisplayItemList.h
+++ b/Source/platform/graphics/paint/DisplayItemList.h
@@ -10,6 +10,9 @@
 #include "platform/graphics/paint/DisplayItems.h"
 #include "wtf/HashMap.h"
 #include "wtf/PassOwnPtr.h"
+#include "wtf/StdLibExtras.h"
+#include "wtf/TypeTraits.h"
+#include "wtf/Utility.h"
 #include "wtf/Vector.h"
 
 namespace blink {
@@ -30,7 +33,14 @@ public:
     void invalidateAll();
 
     // These methods are called during painting.
-    void add(WTF::PassOwnPtr<DisplayItem>);
+
+    template <typename DisplayItemClass, typename... Args>
+    void createAndAppendIfNeeded(Args&&... args)
+    {

[Xianzhu, 2015/06/19 16:19:11]

Can we put displayItemConstructionIsDisabled() check here so that we can the
call to it before each createAndAppendIfNeeded?

+        DisplayItemClass& displayItem = m_newDisplayItems.emplaceBack<DisplayItemClass>(WTF::forward<Args>(args)...);
+        processNewItem(displayItem);
+    }
+
     void beginScope(DisplayItemClient);
     void endScope(DisplayItemClient);
 
@@ -77,6 +87,10 @@ private:
     friend class DisplayItemListPaintTest;
     friend class LayoutObjectDrawingRecorderTest;
 
+
+    // Adjust the list as necessary for newly appended items.
+    void processNewItem(DisplayItem&);
+
     void updateValidlyCachedClientsIfNeeded() const;
 
 #ifndef NDEBUG