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

Source/platform/graphics/paint/FixedPositionDisplayItem.cpp

Index: Source/platform/graphics/paint/FixedPositionDisplayItem.cpp
diff --git a/Source/platform/graphics/paint/FixedPositionDisplayItem.cpp b/Source/platform/graphics/paint/FixedPositionDisplayItem.cpp
index cf19006ebcba883f51c1053e5c7e9f6d8173f5ce..cbf712d0fba677f8479f5edc193647cdd2c910c5 100644
--- a/Source/platform/graphics/paint/FixedPositionDisplayItem.cpp
+++ b/Source/platform/graphics/paint/FixedPositionDisplayItem.cpp
@@ -6,6 +6,7 @@
 #include "platform/graphics/paint/FixedPositionDisplayItem.h"
 
 #include "platform/graphics/GraphicsContext.h"
+#include "platform/graphics/paint/DisplayItems.h"
 #include "platform/transforms/AffineTransform.h"
 #include "public/platform/WebDisplayItemList.h"
 
@@ -16,9 +17,21 @@ void BeginFixedPositionDisplayItem::appendToWebDisplayItemList(WebDisplayItemLis
     // TODO(trchen): Should implement the compositor counterpart and update transform tree algorithm.
 }
 
+void BeginFixedPositionDisplayItem::appendByMoving(DisplayItems& destination)
+{
+    destination.emplaceBack<BeginFixedPositionDisplayItem>(
+        DisplayItemClientWrapperHelper(*this));
+}
+
 void EndFixedPositionDisplayItem::appendToWebDisplayItemList(WebDisplayItemList* list) const
 {
     // TODO(trchen): Should implement the compositor counterpart and update transform tree algorithm.
 }
 
+void EndFixedPositionDisplayItem::appendByMoving(DisplayItems& destination)
+{
+    destination.emplaceBack<EndFixedPositionDisplayItem>(
+        DisplayItemClientWrapperHelper(*this));
+}
+
 } // namespace blink