Generate scroll/clip display item hierarchy for SPv2

Source/platform/graphics/paint/DisplayItemPropertyTreeBuilder.h

Index: Source/platform/graphics/paint/DisplayItemPropertyTreeBuilder.h
diff --git a/Source/platform/graphics/paint/DisplayItemPropertyTreeBuilder.h b/Source/platform/graphics/paint/DisplayItemPropertyTreeBuilder.h
index 9026e07ff3a158c697e0de0ae3287ee4049e600d..e2e9854e6e39baaf937aef80e7690d5519098d95 100644
--- a/Source/platform/graphics/paint/DisplayItemPropertyTreeBuilder.h
+++ b/Source/platform/graphics/paint/DisplayItemPropertyTreeBuilder.h
@@ -7,6 +7,8 @@
 
 #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"
@@ -95,6 +97,8 @@ private:
     // Handle an end display item.
     void processEndItem(const DisplayItem&);
 
+    void processAnchorItem(const DisplayItem&);
+
     // Emit a range record, unless it would be empty.
     void finishRange();
 
@@ -103,6 +107,7 @@ private:
     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;
 };