Generate scroll/clip display item hierarchy for SPv2

Source/platform/graphics/paint/FixedPositionContainerDisplayItem.h

Index: Source/platform/graphics/paint/FixedPositionContainerDisplayItem.h
diff --git a/Source/platform/graphics/paint/FixedPositionContainerDisplayItem.h b/Source/platform/graphics/paint/FixedPositionContainerDisplayItem.h
index 8669ea9abf35e364abc3015151a4c6fffb071b5a..66e658b1081776a6254fa13a1076126793a52126 100644
--- a/Source/platform/graphics/paint/FixedPositionContainerDisplayItem.h
+++ b/Source/platform/graphics/paint/FixedPositionContainerDisplayItem.h
@@ -11,29 +11,15 @@
 
 namespace blink {
 
-class PLATFORM_EXPORT BeginFixedPositionContainerDisplayItem final : public PairedBeginDisplayItem {
+class PLATFORM_EXPORT FixedPositionContainerDisplayItem final : public DisplayItem {
 public:
-    BeginFixedPositionContainerDisplayItem(const DisplayItemClientWrapper& client)
-        : PairedBeginDisplayItem(client, BeginFixedPositionContainer, sizeof(*this)) { }
+    FixedPositionContainerDisplayItem(const DisplayItemClientWrapper& client)
+        : DisplayItem(client, FixedPositionContainer, sizeof(*this)) { }
 
     void replay(GraphicsContext&) final { }
     void appendToWebDisplayItemList(WebDisplayItemList*) const final;
 };
 
-class PLATFORM_EXPORT EndFixedPositionContainerDisplayItem final : public PairedEndDisplayItem {
-public:
-    EndFixedPositionContainerDisplayItem(const DisplayItemClientWrapper& client)
-        : PairedEndDisplayItem(client, EndFixedPositionContainer, sizeof(*this)) { }
-
-    void replay(GraphicsContext&) final { }
-    void appendToWebDisplayItemList(WebDisplayItemList*) const final;
-
-private:
-#if ENABLE(ASSERT)
-    bool isEndAndPairedWith(DisplayItem::Type otherType) const final { return otherType == BeginFixedPositionContainer; }
-#endif
-};
-
 } // namespace blink
 
 #endif // FixedPositionContainerDisplayItem_h