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

Source/platform/graphics/paint/ScrollDisplayItem.cpp

Index: Source/platform/graphics/paint/ScrollDisplayItem.cpp
diff --git a/Source/platform/graphics/paint/ScrollDisplayItem.cpp b/Source/platform/graphics/paint/ScrollDisplayItem.cpp
index 77efe28d451e26c476329ed7d7ff2cbed67b6830..91e756d2f9ec4c12cd161deb01866559cfad1b17 100644
--- a/Source/platform/graphics/paint/ScrollDisplayItem.cpp
+++ b/Source/platform/graphics/paint/ScrollDisplayItem.cpp
@@ -6,6 +6,7 @@
 #include "platform/graphics/paint/ScrollDisplayItem.h"
 
 #include "platform/graphics/GraphicsContext.h"
+#include "platform/graphics/paint/DisplayItems.h"
 #include "platform/transforms/AffineTransform.h"
 #include "public/platform/WebDisplayItemList.h"
 
@@ -23,6 +24,12 @@ void BeginScrollDisplayItem::appendToWebDisplayItemList(WebDisplayItemList* list
     list->appendScrollItem(m_currentOffset, scrollContainerId);
 }
 
+void BeginScrollDisplayItem::appendByMoving(DisplayItems& destination)
+{
+    destination.emplaceBack<BeginScrollDisplayItem>(
+        DisplayItemClientWrapperHelper(*this), type(), m_currentOffset);
+}
+
 #ifndef NDEBUG
 void BeginScrollDisplayItem::dumpPropertiesAsDebugString(WTF::StringBuilder& stringBuilder) const
 {
@@ -41,4 +48,10 @@ void EndScrollDisplayItem::appendToWebDisplayItemList(WebDisplayItemList* list)
     list->appendEndScrollItem();
 }
 
+void EndScrollDisplayItem::appendByMoving(DisplayItems& destination)
+{
+    destination.emplaceBack<EndScrollDisplayItem>(
+        DisplayItemClientWrapperHelper(*this), type());
+}
+
 } // namespace blink