Oilpan: Remove guardRef and guardDeref from TreeScope.

Source/core/page/FocusController.h

Index: Source/core/page/FocusController.h
diff --git a/Source/core/page/FocusController.h b/Source/core/page/FocusController.h
index 0983fcd5ce7589873dd3aef13ca5b4b72750fd37..a4f99b0abe886ceafad8ba9ce62e0c138852f606 100644
--- a/Source/core/page/FocusController.h
+++ b/Source/core/page/FocusController.h
@@ -27,6 +27,7 @@
 #define FocusController_h
 
 #include "core/page/FocusType.h"
+#include "heap/Handle.h"
 #include "platform/geometry/LayoutRect.h"
 #include "wtf/Forward.h"
 #include "wtf/Noncopyable.h"
@@ -47,6 +48,7 @@ class Page;
 class TreeScope;
 
 class FocusNavigationScope {
+    STACK_ALLOCATED();
 public:
     Node* rootNode() const;
     Element* owner() const;
@@ -58,7 +60,7 @@ public:
 
 private:
     explicit FocusNavigationScope(TreeScope*);
-    TreeScope* m_rootTreeScope;
+    RawPtrWillBeMember<TreeScope> m_rootTreeScope;
 };
 
 class FocusController {