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

Source/platform/graphics/paint/SubtreeDisplayItem.h

Index: Source/platform/graphics/paint/SubtreeDisplayItem.h
diff --git a/Source/platform/graphics/paint/SubtreeDisplayItem.h b/Source/platform/graphics/paint/SubtreeDisplayItem.h
index efddb5edab88a954e084b6139d750d0964461f53..64c0a28d39d3104cda512c4f4dd5264dc077247c 100644
--- a/Source/platform/graphics/paint/SubtreeDisplayItem.h
+++ b/Source/platform/graphics/paint/SubtreeDisplayItem.h
@@ -19,15 +19,16 @@ public:
         return adoptPtr(new SubtreeCachedDisplayItem(client, type));
     }
 
-private:
     SubtreeCachedDisplayItem(const DisplayItemClientWrapper& client, Type type)
         : DisplayItem(client, type)
     {
         ASSERT(isSubtreeCachedType(type));
     }
 
+private:
     virtual void replay(GraphicsContext&) override final { ASSERT_NOT_REACHED(); }
     virtual void appendToWebDisplayItemList(WebDisplayItemList*) const override final { ASSERT_NOT_REACHED(); }
+    virtual void appendByMoving(DisplayItems&) override;
 };
 
 class PLATFORM_EXPORT BeginSubtreeDisplayItem : public PairedBeginDisplayItem {
@@ -38,7 +39,8 @@ public:
         return adoptPtr(new BeginSubtreeDisplayItem(client, type));
     }
 
-private:
+    virtual void appendByMoving(DisplayItems&) override;
+
     BeginSubtreeDisplayItem(const DisplayItemClientWrapper& client, Type type)
         : PairedBeginDisplayItem(client, type)
     {
@@ -54,7 +56,8 @@ public:
         return adoptPtr(new EndSubtreeDisplayItem(client, type));
     }
 
-private:
+    virtual void appendByMoving(DisplayItems&) override;
+
     EndSubtreeDisplayItem(const DisplayItemClientWrapper& client, Type type)
         : PairedEndDisplayItem(client, type)
     {