Oilpan: Replace RefPtrs to Node and its subclasses in core/xml/ with Oilpan transition types.

Source/core/xml/XPathExpressionNode.h

Index: Source/core/xml/XPathExpressionNode.h
diff --git a/Source/core/xml/XPathExpressionNode.h b/Source/core/xml/XPathExpressionNode.h
index c7f876ce84ad01c96029c02bfd83723dd1b2478d..959c88411c696efbefd2eb4b2954a99693392fa6 100644
--- a/Source/core/xml/XPathExpressionNode.h
+++ b/Source/core/xml/XPathExpressionNode.h
@@ -40,7 +40,7 @@ namespace WebCore {
         struct EvaluationContext {
             WTF_MAKE_FAST_ALLOCATED;
         public:
-            RefPtr<Node> node;
+            RefPtrWillBePersistent<Node> node;
             unsigned long size;
             unsigned long position;
             HashMap<String, String> variableBindings;