WIP for display item list backed by ListContainer

Source/platform/graphics/paint/ScrollDisplayItem.h

Index: Source/platform/graphics/paint/ScrollDisplayItem.h
diff --git a/Source/platform/graphics/paint/ScrollDisplayItem.h b/Source/platform/graphics/paint/ScrollDisplayItem.h
index b3326608608d5d1f8b295d72bd5b2177d549b04a..de2f908b6cd43335ff9617a05bfca484f0e86018 100644
--- a/Source/platform/graphics/paint/ScrollDisplayItem.h
+++ b/Source/platform/graphics/paint/ScrollDisplayItem.h
@@ -13,18 +13,11 @@
 namespace blink {
 
 class PLATFORM_EXPORT BeginScrollDisplayItem : public PairedBeginDisplayItem {
-    WTF_MAKE_FAST_ALLOCATED(BeginScrollDisplayItem);
 public:
-    static PassOwnPtr<BeginScrollDisplayItem> create(const DisplayItemClientWrapper& client, Type type, const IntSize& currentOffset)
+    void setNew(IntSize& currentOffset)
     {
-        return adoptPtr(new BeginScrollDisplayItem(client, type, currentOffset));
-    }
-
-    BeginScrollDisplayItem(const DisplayItemClientWrapper& client, Type type, const IntSize& currentOffset)
-        : PairedBeginDisplayItem(client, type)
-        , m_currentOffset(currentOffset)
-    {
-        ASSERT(isScrollType(type));
+        m_currentOffset = currentOffset;
+        ASSERT(isScrollType(type()));
     }
 
     virtual void replay(GraphicsContext&) override;
@@ -35,23 +28,11 @@ private:
     virtual void dumpPropertiesAsDebugString(WTF::StringBuilder&) const override final;
 #endif
 
-    const IntSize m_currentOffset;
+    IntSize m_currentOffset;
 };
 
 class PLATFORM_EXPORT EndScrollDisplayItem : public PairedEndDisplayItem {
-    WTF_MAKE_FAST_ALLOCATED(EndScrollDisplayItem);
 public:
-    static PassOwnPtr<EndScrollDisplayItem> create(const DisplayItemClientWrapper& client, Type type)
-    {
-        return adoptPtr(new EndScrollDisplayItem(client, type));
-    }
-
-    EndScrollDisplayItem(const DisplayItemClientWrapper& client, Type type)
-        : PairedEndDisplayItem(client, type)
-    {
-        ASSERT(isEndScrollType(type));
-    }
-
     virtual void replay(GraphicsContext&) override;
     virtual void appendToWebDisplayItemList(WebDisplayItemList*) const override;