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

Source/WebKit/chromium/src/WebSettingsImpl.cpp

 /*
  * Copyright (C) 2009 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 438 matching lines @@
 }
 
 void WebSettingsImpl::setAcceleratedCompositingForVideoEnabled(bool enabled)
 {
     m_settings->setAcceleratedCompositingForVideoEnabled(enabled);
 }
 
 void WebSettingsImpl::setAcceleratedCompositingForOverflowScrollEnabled(
     bool enabled)
 {
-    m_settings->setAcceleratedCompositingForOverflowScrollEnabled(enabled);
+    // FIXME: we may want to plumb a tri state all the way to the browser so
+    // we can expose it via about:flags.
+    AcceleratedCompositingForOverflowScrollEnabledMode mode = enabled
+        ? AcceleratedCompositingForOverflowScrollEnabled
+        : AcceleratedCompositingForOverflowScrollDisabled;
+
+    m_settings->setAcceleratedCompositingForOverflowScrollEnabled(mode);
 }
 
 void WebSettingsImpl::setAcceleratedCompositingForPluginsEnabled(bool enabled)
 {
     m_settings->setAcceleratedCompositingForPluginsEnabled(enabled);
 }
 
 void WebSettingsImpl::setAcceleratedCompositingForCanvasEnabled(bool enabled)
 {
     m_settings->setAcceleratedCompositingForCanvasEnabled(enabled);
@@ skipping 213 matching lines @@
 {
     m_settings->setSelectionIncludesAltImageText(enabled);
 }
 
 void WebSettingsImpl::setSmartInsertDeleteEnabled(bool enabled)
 {
     m_settings->setSmartInsertDeleteEnabled(enabled);
 }
 
 } // namespace WebKit