[Slimming Paint] 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..f8335f42b55b43c56fb4107b07722b8e13296dd0 100644
--- a/Source/platform/graphics/paint/DisplayItemList.h
+++ b/Source/platform/graphics/paint/DisplayItemList.h
@@ -30,7 +30,11 @@ public:
     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);