Delete AXObjectCache when disabling accessibility setting.

Source/core/frame/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 114 matching lines @@
 
 void Settings::setOpenGLMultisamplingEnabled(bool flag)
 {
     if (m_openGLMultisamplingEnabled == flag)
         return;
 
     m_openGLMultisamplingEnabled = flag;
     invalidate(SettingsDelegate::MultisamplingChange);
 }
 
+void Settings::setAccessibilityEnabled(bool flag)
+{
+    if (m_accessibilityEnabled == flag)
+        return;
+
+    m_accessibilityEnabled = flag;
+    invalidate(SettingsDelegate::AccessibilityStateChange);
+}
+
 } // namespace blink