Make composited scrolling codepaths co-operate.

Source/core/page/Settings.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2011, 2012 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 121 matching lines @@
     , m_loadsImagesAutomatically(false)
     , m_areImagesEnabled(true)
     , m_arePluginsEnabled(false)
     , m_isScriptEnabled(false)
     , m_isCSSCustomFilterEnabled(false)
     , m_cssStickyPositionEnabled(true)
     , m_dnsPrefetchingEnabled(false)
     , m_touchEventEmulationEnabled(false)
     , m_viewportEnabled(false)
     , m_setImageLoadingSettingsTimer(this, &Settings::imageLoadingSettingsTimerFired)
-    , m_compositorDrivenAcceleratedScrollingEnabled(false)
+    , m_compositorDrivenAcceleratedScrollingEnabled(true)
 {
     m_page = page; // Page is not yet fully initialized wen constructing Settings, so keeping m_page null over initializeDefaultFontFamilies() call.
 }
 
 PassOwnPtr<Settings> Settings::create(Page* page)
 {
     return adoptPtr(new Settings(page));
 }
 
 SETTINGS_SETTER_BODIES
@@ skipping 233 matching lines @@
 {
     if (m_viewportEnabled == enabled)
         return;
 
     m_viewportEnabled = enabled;
     if (m_page->mainFrame())
         m_page->mainFrame()->document()->updateViewportArguments();
 }
 
 } // namespace WebCore