Rename usesOverlayScrollbars of settings to mockScrollbarsUseOverlay

Source/core/testing/Internals.idl

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  * Copyright (C) 2013 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.
@@ skipping 230 matching lines @@
     // Returns a string with information about the mouse cursor used at the specified client location.
     [RaisesException] DOMString getCurrentCursorInfo(Document document);
 
     [RaisesException] DOMString markerTextForListItem(Element element);
 
     [RaisesException] DOMString baseURL(Document document);
 
     SerializedScriptValue deserializeBuffer(ArrayBuffer buffer);
     ArrayBuffer serializeObject(SerializedScriptValue obj);
 
-    void setUsesOverlayScrollbars(boolean enabled);
-
     void forceReload(boolean endToEnd);
 
     void enableMockSpeechSynthesizer();
 
     [RaisesException] DOMString getImageSourceURL(Element element);
 
     boolean isSelectPopupVisible(Node node);
 
     [RaisesException] ClientRect selectionBounds();
 
     boolean loseSharedGraphicsContext3D();
 };