WIP (Introduce WTF::NonNullPtr<T>.)

Source/core/dom/EventRetargeter.h

Index: Source/core/dom/EventRetargeter.h
diff --git a/Source/core/dom/EventRetargeter.h b/Source/core/dom/EventRetargeter.h
index ea5b36e8c81535e4661af80ec0ff3eb2e36a13eb..c76c0be7e310fd5775f0e31f62ebcf16aa1e2341 100644
--- a/Source/core/dom/EventRetargeter.h
+++ b/Source/core/dom/EventRetargeter.h
@@ -81,7 +81,7 @@ inline EventTarget* EventRetargeter::eventTargetRespectingTargetRules(Node* refe
 
     // Spec: The event handling for the non-exposed tree works as if the referenced element had been textually included
     // as a deeply cloned child of the 'use' element, except that events are dispatched to the SVGElementInstance objects.
-    Node* rootNode = referenceNode->treeScope().rootNode();
+    Node* rootNode = referenceNode->treeScope()->rootNode();
     Element* shadowHostElement = rootNode->isShadowRoot() ? toShadowRoot(rootNode)->host() : 0;
     // At this time, SVG nodes are not supported in non-<use> shadow trees.
     if (!shadowHostElement || !shadowHostElement->hasTagName(SVGNames::useTag))