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

third_party/WebKit/Source/core/layout/LayoutThemeDefault.cpp

 /*
  * Copyright (C) 2007 Apple Inc.
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  * Copyright (C) 2008 Collabora Ltd.
  * Copyright (C) 2008, 2009 Google Inc.
  * Copyright (C) 2009 Kenneth Rohde Christiansen
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 372 matching lines @@
 }
 
 // static
 void LayoutThemeDefault::setDefaultFontSize(int fontSize)
 {
     LayoutThemeFontProvider::setDefaultFontSize(fontSize);
 }
 
 int LayoutThemeDefault::menuListArrowPadding() const
 {
-    return ScrollbarTheme::theme()->scrollbarThickness();
+    return ScrollbarTheme::theme().scrollbarThickness();
 }
 
 int LayoutThemeDefault::menuListInternalPadding(const ComputedStyle& style, int paddingType) const
 {
     if (style.appearance() == NoControlPart)
         return 0;
     // This internal padding is in addition to the user-supplied padding.
     // Matches the FF behavior.
     int padding = styledMenuListInternalPadding[paddingType];
 
@@ skipping 17 matching lines @@
 {
     return progressAnimationInterval;
 }
 
 double LayoutThemeDefault::animationDurationForProgressBar() const
 {
     return progressAnimationInterval * progressAnimationFrames * 2; // "2" for back and forth
 }
 
 } // namespace blink