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

Source/platform/graphics/paint/FixedPositionContainerDisplayItem.cpp

Index: Source/platform/graphics/paint/FixedPositionContainerDisplayItem.cpp
diff --git a/Source/platform/graphics/paint/FixedPositionContainerDisplayItem.cpp b/Source/platform/graphics/paint/FixedPositionContainerDisplayItem.cpp
index a0c5b82118f6ef98785d7475088c9ba90351eab9..da56dd3d455ac6d56ef3711f3376946eedaafd1e 100644
--- a/Source/platform/graphics/paint/FixedPositionContainerDisplayItem.cpp
+++ b/Source/platform/graphics/paint/FixedPositionContainerDisplayItem.cpp
@@ -6,6 +6,7 @@
 #include "platform/graphics/paint/FixedPositionContainerDisplayItem.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 BeginFixedPositionContainerDisplayItem::appendToWebDisplayItemList(WebDispl
     // TODO(trchen): Should implement the compositor counterpart and update transform tree algorithm.
 }
 
+void BeginFixedPositionContainerDisplayItem::appendByMoving(DisplayItems& destination)
+{
+    destination.emplaceBack<BeginFixedPositionContainerDisplayItem>(
+        DisplayItemClientWrapperHelper(*this));
+}
+
 void EndFixedPositionContainerDisplayItem::appendToWebDisplayItemList(WebDisplayItemList* list) const
 {
     // TODO(trchen): Should implement the compositor counterpart and update transform tree algorithm.
 }
 
+void EndFixedPositionContainerDisplayItem::appendByMoving(DisplayItems& destination)
+{
+    destination.emplaceBack<EndFixedPositionContainerDisplayItem>(
+        DisplayItemClientWrapperHelper(*this));
+}
+
 } // namespace blink