Clean up the way layout tests force elements to opt in/out of composited scrolling.

Source/core/page/Settings.h

 /*
  * Copyright (C) 2003, 2006, 2007, 2008, 2009, 2011, 2012 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *
  * 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
@@ skipping 38 matching lines @@
     EditableLinkLiveWhenNotFocused,
     EditableLinkNeverLive
 };
 
 enum TextDirectionSubmenuInclusionBehavior {
     TextDirectionSubmenuNeverIncluded,
     TextDirectionSubmenuAutomaticallyIncluded,
     TextDirectionSubmenuAlwaysIncluded
 };
 
+enum AcceleratedCompositingForOverflowScrollEnabledMode {
+    AcceleratedCompositingForOverflowScrollDisabled = 0,
+    AcceleratedCompositingForOverflowScrollEnabled = 1,
+    AcceleratedCompositingForOverflowScrollAlwaysOn = 2
+};
+
 // UScriptCode uses -1 and 0 for UScriptInvalidCode and UScriptCommon.
 // We need to use -2 and -3 for empty value and deleted value.
 struct UScriptCodeHashTraits : WTF::GenericHashTraits<int> {
     static const bool emptyValueIsZero = false;
     static int emptyValue() { return -2; }
     static void constructDeletedValue(int& slot) { slot = -3; }
     static bool isDeletedValue(int value) { return value == -3; }
 };
 
 typedef HashMap<int, AtomicString, DefaultHash<int>::Hash, UScriptCodeHashTraits> ScriptFontFamilyMap;
@@ skipping 130 matching lines @@
     Timer<Settings> m_setImageLoadingSettingsTimer;
     void imageLoadingSettingsTimerFired(Timer<Settings>*);
 
     static bool gMockScrollbarsEnabled;
     static bool gUsesOverlayScrollbars;
 };
 
 } // namespace WebCore
 
 #endif // Settings_h