[WIP] Use the flat tree for hover handling.

third_party/WebKit/Source/core/dom/Document.h

Index: third_party/WebKit/Source/core/dom/Document.h
diff --git a/third_party/WebKit/Source/core/dom/Document.h b/third_party/WebKit/Source/core/dom/Document.h
index a96d14e8b2663a4cc816efcef9e84012ca6c020c..92565f85932f23ca3280307b6228befb8f8aa1fd 100644
--- a/third_party/WebKit/Source/core/dom/Document.h
+++ b/third_party/WebKit/Source/core/dom/Document.h
@@ -708,7 +708,7 @@ class CORE_EXPORT Document : public ContainerNode,
   void setActiveHoverElement(Element*);
   Element* activeHoverElement() const { return m_activeHoverElement.get(); }
 
-  Node* hoverNode() const { return m_hoverNode.get(); }
+  Element* hoverElement() const { return m_hoverElement.get(); }
 
   void removeFocusedElementOfSubtree(Node*, bool amongChildrenOnly = false);
   void hoveredNodeDetached(Element&);
@@ -1400,7 +1400,7 @@ class CORE_EXPORT Document : public ContainerNode,
   bool haveRenderBlockingStylesheetsLoaded() const;
   void styleResolverMayHaveChanged();
 
-  void setHoverNode(Node*);
+  void setHoverElement(Element*);
 
   using EventFactorySet = HashSet<std::unique_ptr<EventFactoryBase>>;
   static EventFactorySet& eventFactories();
@@ -1475,7 +1475,7 @@ class CORE_EXPORT Document : public ContainerNode,
   Member<Element> m_autofocusElement;
   Member<Element> m_focusedElement;
   Member<Range> m_sequentialFocusNavigationStartingPoint;
-  Member<Node> m_hoverNode;
+  Member<Element> m_hoverElement;
   Member<Element> m_activeHoverElement;
   Member<Element> m_documentElement;
   UserActionElementSet m_userActionElements;