Rename usesOverlayScrollbars of settings to mockScrollbarsUseOverlay

Source/core/platform/mock/ScrollbarThemeMock.h

 /*
  * 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 16 matching lines @@
 #define ScrollbarThemeMock_h
 
 #include "core/platform/ScrollbarTheme.h"
 
 namespace WebCore {
 
 // Scrollbar theme used in image snapshots, to eliminate appearance differences between platforms.
 class ScrollbarThemeMock : public ScrollbarTheme {
 public:
     virtual int scrollbarThickness(ScrollbarControlSize = RegularScrollbar) OVERRIDE;
-    virtual bool usesOverlayScrollbars() const OVERRIDE;
 
 protected:
     virtual bool hasButtons(ScrollbarThemeClient*) OVERRIDE { return false; }
     virtual bool hasThumb(ScrollbarThemeClient*) OVERRIDE { return true; }
 
     virtual IntRect backButtonRect(ScrollbarThemeClient*, ScrollbarPart, bool /*painting*/ = false) OVERRIDE { return IntRect(); }
     virtual IntRect forwardButtonRect(ScrollbarThemeClient*, ScrollbarPart, bool /*painting*/ = false) OVERRIDE { return IntRect(); }
     virtual IntRect trackRect(ScrollbarThemeClient*, bool painting = false) OVERRIDE;
 
     virtual void paintTrackBackground(GraphicsContext*, ScrollbarThemeClient*, const IntRect&) OVERRIDE;
     virtual void paintThumb(GraphicsContext*, ScrollbarThemeClient*, const IntRect&) OVERRIDE;
 
 private:
     virtual bool isMockTheme() const OVERRIDE FINAL { return true; }
 };
 
 }
 #endif // ScrollbarThemeMock_h