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

third_party/WebKit/Source/platform/scroll/ScrollbarThemeMacNonOverlayAPI.h

 /*
  * Copyright (C) 2013 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 25 matching lines @@
 namespace blink {
 
 class CullRect;
 
 class PLATFORM_EXPORT ScrollbarThemeMacNonOverlayAPI : public ScrollbarThemeMacCommon {
 public:
     int scrollbarThickness(ScrollbarControlSize = RegularScrollbar) override;
     bool usesOverlayScrollbars() const override { return false; }
     ScrollbarButtonsPlacement buttonsPlacement() const override;
 
-    bool paint(const ScrollbarThemeClient*, GraphicsContext*, const CullRect&) override;
+    bool paint(const ScrollbarThemeClient&, GraphicsContext&, const CullRect&) override;
     bool invalidateOnWindowActiveChange() const override { return true; }
 
 protected:
-    IntRect trackRect(const ScrollbarThemeClient*, bool painting = false) override;
-    IntRect backButtonRect(const ScrollbarThemeClient*, ScrollbarPart, bool painting = false) override;
-    IntRect forwardButtonRect(const ScrollbarThemeClient*, ScrollbarPart, bool painting = false) override;
+    IntRect trackRect(const ScrollbarThemeClient&, bool painting = false) override;
+    IntRect backButtonRect(const ScrollbarThemeClient&, ScrollbarPart, bool painting = false) override;
+    IntRect forwardButtonRect(const ScrollbarThemeClient&, ScrollbarPart, bool painting = false) override;
 
     void updateButtonPlacement(ScrollbarButtonsPlacement) override;
 
-    bool hasButtons(const ScrollbarThemeClient*) override;
-    bool hasThumb(const ScrollbarThemeClient*) override;
+    bool hasButtons(const ScrollbarThemeClient&) override;
+    bool hasThumb(const ScrollbarThemeClient&) override;
 
-    int minimumThumbLength(const ScrollbarThemeClient*) override;
+    int minimumThumbLength(const ScrollbarThemeClient&) override;
 };
 
 }
 
 #endif