Oilpan: tidy up definition of some stack-allocated scope objects.

Source/core/dom/NodeRenderingTraversal.h

Index: Source/core/dom/NodeRenderingTraversal.h
diff --git a/Source/core/dom/NodeRenderingTraversal.h b/Source/core/dom/NodeRenderingTraversal.h
index 623343a54e4df4dd2bbe2b39fc4153325643e325..a54b10214a23ab3ebe90c6c8655c95a0ec4b901a 100644
--- a/Source/core/dom/NodeRenderingTraversal.h
+++ b/Source/core/dom/NodeRenderingTraversal.h
@@ -37,9 +37,10 @@ class RenderObject;
 namespace NodeRenderingTraversal {
 
 class ParentDetails {
+    STACK_ALLOCATED();
 public:
     ParentDetails()
-        : m_insertionPoint(0)
+        : m_insertionPoint(nullptr)
     { }
 
     const InsertionPoint* insertionPoint() const { return m_insertionPoint; }
@@ -52,7 +53,7 @@ public:
     }
 
 private:
-    const InsertionPoint* m_insertionPoint;
+    RawPtrWillBeMember<const InsertionPoint> m_insertionPoint;
 };
 
 ContainerNode* parent(const Node&, ParentDetails* = 0);