Rename usesOverlayScrollbars of settings to mockScrollbarsUseOverlay

Source/core/platform/mock/ScrollbarThemeMock.cpp

 /*
  * Copyright (C) 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
@@ skipping 24 matching lines @@
 IntRect ScrollbarThemeMock::trackRect(ScrollbarThemeClient* scrollbar, bool)
 {
     return scrollbar->frameRect();
 }
 
 int ScrollbarThemeMock::scrollbarThickness(ScrollbarControlSize controlSize)
 {
     return cScrollbarThickness[controlSize];
 }
 
-bool ScrollbarThemeMock::usesOverlayScrollbars() const
-{
-    return Settings::usesOverlayScrollbars();
-}
-
 void ScrollbarThemeMock::paintTrackBackground(GraphicsContext* context, ScrollbarThemeClient* scrollbar, const IntRect& trackRect)
 {
     context->fillRect(trackRect, scrollbar->enabled() ? Color::lightGray : Color(0xFFE0E0E0));
 }
 
 void ScrollbarThemeMock::paintThumb(GraphicsContext* context, ScrollbarThemeClient* scrollbar, const IntRect& thumbRect)
 {
     if (scrollbar->enabled())
         context->fillRect(thumbRect, Color::darkGray);
 }
 
 }