Lazy evaluation of event.path by numbering TreeScopes in DFS order for later O(1) queries

Source/core/events/Event.cpp

Index: Source/core/events/Event.cpp
diff --git a/Source/core/events/Event.cpp b/Source/core/events/Event.cpp
index 1111b1570713cfa484a2178ec37244750c237fad..043b3051f2613fe8d9d16628a60845e85084ffc4 100644
--- a/Source/core/events/Event.cpp
+++ b/Source/core/events/Event.cpp
@@ -202,11 +202,13 @@ PassRefPtr<NodeList> Event::path() const
     if (!m_currentTarget || !m_currentTarget->toNode())
         return StaticNodeList::createEmpty();
     Node* node = m_currentTarget->toNode();
+    // FIXME: Support SVG Elements.
+    if (node->isSVGElement())
+        return StaticNodeList::createEmpty();
     size_t eventPathSize = m_eventPath->size();
     for (size_t i = 0; i < eventPathSize; ++i) {
         if (node == (*m_eventPath)[i].node()) {
-            ASSERT((*m_eventPath)[i].eventPath());
-            return (*m_eventPath)[i].eventPath();
+            return (*m_eventPath)[i].treeScopeEventContext()->ensureEventPath(*m_eventPath);
         }
     }
     return StaticNodeList::createEmpty();