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

Source/core/paint/DisplayItemListPaintTest.cpp

Index: Source/core/paint/DisplayItemListPaintTest.cpp
diff --git a/Source/core/paint/DisplayItemListPaintTest.cpp b/Source/core/paint/DisplayItemListPaintTest.cpp
index 4ccac96c24c32f3dfa60ceb578a338fee83cd637..4e6ba3d490ee6e9bf5ebaa9db27fff6b78046465 100644
--- a/Source/core/paint/DisplayItemListPaintTest.cpp
+++ b/Source/core/paint/DisplayItemListPaintTest.cpp
@@ -61,6 +61,12 @@ public:
 
     virtual void replay(GraphicsContext&) override final { ASSERT_NOT_REACHED(); }
     virtual void appendToWebDisplayItemList(WebDisplayItemList*) const override final { ASSERT_NOT_REACHED(); }
+
+    void appendByMoving(DisplayItems& destination) override
+    {
+        destination.emplaceBack<TestDisplayItem>(
+            DisplayItemClientWrapperHelper(*this), type());
+    }
 };
 
 #ifndef NDEBUG