Implement a Hit Test Cache.

Source/core/dom/TreeScope.h

Index: Source/core/dom/TreeScope.h
diff --git a/Source/core/dom/TreeScope.h b/Source/core/dom/TreeScope.h
index 1bfcdf91861bd05cc0b548b98cc7eebc3ba2422e..30b28b8cec1c66b394ac366028b6b95f5dff30f6 100644
--- a/Source/core/dom/TreeScope.h
+++ b/Source/core/dom/TreeScope.h
@@ -77,6 +77,7 @@ public:
     HTMLMapElement* getImageMap(const String& url) const;
 
     Element* elementFromPoint(int x, int y) const;
+    Element* elementFromPointNoCache(int x, int y) const;
     Vector<Element*> elementsFromPoint(int x, int y) const;
 
     // For accessibility.
@@ -176,6 +177,9 @@ private:
 
     bool rootNodeHasTreeSharedParent() const;
 
+    // Return the element from the point |x,y| and conditionally use the cache based on |useCache|.
+    Element* hitTestPoint(int x, int y, bool useCache) const;

[esprehn, 2015/06/06 21:14:29]

Can we use an IntPoint?

[dtapuska, 2015/06/09 18:21:23]

We could; but I think this would be overkill. Since the implementation of this
method does in fact create a IntPoint it would make sense at first; but the
implementation actually modifies the IntPoint; so we'd still need to make a copy
of the IntPoint that was passed in anyways. So passing it intermediately as a
IntPoint just seems like overkill. Let me know if you think otherwise.

+
     RawPtrWillBeMember<ContainerNode> m_rootNode;
     RawPtrWillBeMember<Document> m_document;
     RawPtrWillBeMember<TreeScope> m_parentTreeScope;
@@ -208,7 +212,7 @@ inline bool TreeScope::containsMultipleElementsWithId(const AtomicString& id) co
 
 DEFINE_COMPARISON_OPERATORS_WITH_REFERENCES(TreeScope)
 
-HitTestResult hitTestInDocument(const Document*, int x, int y);
+HitTestResult hitTestInDocument(const Document*, int x, int y, bool useCache);
 
 } // namespace blink