Use refs for non-null GraphicsContext, Scrollbar, etc. in scrollbar related code

third_party/WebKit/Source/platform/mac/ScrollAnimatorMac.h

 /*
  * Copyright (C) 2010, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
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     void handleWheelEventPhase(PlatformWheelEventPhase) override;
 
     void cancelAnimations() override;
     void setIsActive() override;
 
     void contentAreaWillPaint() const override;
     void mouseEnteredContentArea() const override;
     void mouseExitedContentArea() const override;
     void mouseMovedInContentArea() const override;
-    void mouseEnteredScrollbar(Scrollbar*) const override;
-    void mouseExitedScrollbar(Scrollbar*) const override;
+    void mouseEnteredScrollbar(Scrollbar&) const override;
+    void mouseExitedScrollbar(Scrollbar&) const override;
     void willStartLiveResize() override;
     void contentsResized() const override;
     void willEndLiveResize() override;
     void contentAreaDidShow() const override;
     void contentAreaDidHide() const override;
     void didBeginScrollGesture() const;
     void didEndScrollGesture() const;
     void mayBeginScrollGesture() const;
 
     void finishCurrentScrollAnimations() override;
 
-    void didAddVerticalScrollbar(Scrollbar*) override;
-    void willRemoveVerticalScrollbar(Scrollbar*) override;
-    void didAddHorizontalScrollbar(Scrollbar*) override;
-    void willRemoveHorizontalScrollbar(Scrollbar*) override;
+    void didAddVerticalScrollbar(Scrollbar&) override;
+    void willRemoveVerticalScrollbar(Scrollbar&) override;
+    void didAddHorizontalScrollbar(Scrollbar&) override;
+    void willRemoveHorizontalScrollbar(Scrollbar&) override;
 
-    bool shouldScrollbarParticipateInHitTesting(Scrollbar*) override;
+    bool shouldScrollbarParticipateInHitTesting(Scrollbar&) override;
 
     void notifyContentAreaScrolled(const FloatSize& delta) override;
 
     bool setScrollbarsVisibleForTesting(bool) override;
 
     FloatPoint adjustScrollPositionIfNecessary(const FloatPoint&) const;
 
     void immediateScrollTo(const FloatPoint&);
 
     bool m_haveScrolledSincePageLoad;
     bool m_needsScrollerStyleUpdate;
     IntRect m_visibleScrollerThumbRect;
 };
 
 } // namespace blink
 
 #endif // ScrollAnimatorMac_h