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

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

 /*
  * Copyright (c) 2008, 2009, 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 19 matching lines @@
 
 #ifndef ScrollbarThemeNonMacCommon_h
 #define ScrollbarThemeNonMacCommon_h
 
 #include "platform/scroll/ScrollbarTheme.h"
 
 namespace blink {
 
 class PLATFORM_EXPORT ScrollbarThemeNonMacCommon : public ScrollbarTheme {
 protected:
-    bool hasButtons(const ScrollbarThemeClient*) override { return true; }
-    bool hasThumb(const ScrollbarThemeClient*) override;
+    bool hasButtons(const ScrollbarThemeClient&) override { return true; }
+    bool hasThumb(const ScrollbarThemeClient&) 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;
+    IntRect trackRect(const ScrollbarThemeClient&, bool painting = false) override;
 
-    void paintTrackBackground(GraphicsContext*, const ScrollbarThemeClient*, const IntRect&) override;
-    void paintTickmarks(GraphicsContext*, const ScrollbarThemeClient*, const IntRect&) override;
+    void paintTrackBackground(GraphicsContext&, const ScrollbarThemeClient&, const IntRect&) override;
+    void paintTickmarks(GraphicsContext&, const ScrollbarThemeClient&, const IntRect&) override;
 
-    virtual IntSize buttonSize(const ScrollbarThemeClient*) = 0;
+    virtual IntSize buttonSize(const ScrollbarThemeClient&) = 0;
 };
 
 } // namespace blink
 
 #endif