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 97ae40264f991a1ff8c2edf735be75a2685725be..3f39ae7eb49deda048435659253146b2112f56e2 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 {