Generate scroll/clip display item hierarchy for SPv2

Source/platform/graphics/paint/DisplayItemPropertyTreeBuilder.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 DisplayItemPropertyTreeBuilder_h
 #define DisplayItemPropertyTreeBuilder_h
 
 #include "platform/PlatformExport.h"
 #include "platform/geometry/FloatSize.h"
+#include "platform/graphics/paint/DisplayItemClient.h"
+#include "wtf/HashMap.h"
 #include "wtf/OwnPtr.h"
 #include "wtf/PassOwnPtr.h"
 #include "wtf/Vector.h"
 
 namespace blink {
 
 class DisplayItem;
 class DisplayItemClipTree;
 class DisplayItemTransformTree;
 
@@ skipping 68 matching lines @@
 
     // Used to manipulate the current transform node stack.
     BuilderState& currentState() { return m_stateStack.last(); }
 
     // Handle a begin display item.
     void processBeginItem(const DisplayItem&);
 
     // Handle an end display item.
     void processEndItem(const DisplayItem&);
 
+    void processAnchorItem(const DisplayItem&);
+
     // Emit a range record, unless it would be empty.
     void finishRange();
 
     OwnPtr<DisplayItemTransformTree> m_transformTree;
     OwnPtr<DisplayItemClipTree> m_clipTree;
     Vector<RangeRecord> m_rangeRecords;
     // TODO(jbroman): Experimentally select a less arbitrary inline capacity.
     Vector<BuilderState, 40> m_stateStack;
+    HashMap<DisplayItemClient, BuilderState> m_anchors;
     size_t m_rangeBeginIndex;
     size_t m_currentIndex;
 };
 
 } // namespace blink
 
 #endif // DisplayItemPropertyTreeBuilder_h