Generate scroll/clip display item hierarchy for SPv2

Source/platform/graphics/paint/FixedPositionContainerDisplayItem.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef FixedPositionContainerDisplayItem_h
 #define FixedPositionContainerDisplayItem_h
 
 #include "platform/geometry/LayoutSize.h"
 #include "platform/graphics/paint/DisplayItem.h"
 #include "wtf/PassOwnPtr.h"
 
 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