Make some arguments of FocusController functions references.

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 95b04f5d701faeb32e43d333db4f3db3b5e0399f..ac06469fc6eb8bb667f7d6bfc150ba01faf33ab7 100644
--- a/Source/core/page/FocusController.h
+++ b/Source/core/page/FocusController.h
@@ -49,11 +49,11 @@ class FocusNavigationScope {
 public:
     Node* rootNode() const;
     Element* owner() const;
-    static FocusNavigationScope focusNavigationScopeOf(Node*);
-    static FocusNavigationScope ownedByNonFocusableFocusScopeOwner(Node*);
-    static FocusNavigationScope ownedByShadowHost(Node*);
-    static FocusNavigationScope ownedByShadowInsertionPoint(HTMLShadowElement*);
-    static FocusNavigationScope ownedByIFrame(HTMLFrameOwnerElement*);
+    static FocusNavigationScope focusNavigationScopeOf(Node&);
+    static FocusNavigationScope ownedByNonFocusableFocusScopeOwner(Node&);
+    static FocusNavigationScope ownedByShadowHost(Node&);
+    static FocusNavigationScope ownedByShadowInsertionPoint(HTMLShadowElement&);
+    static FocusNavigationScope ownedByIFrame(HTMLFrameOwnerElement&);
 
 private:
     explicit FocusNavigationScope(TreeScope*);