Delete AXObjectCache when disabling accessibility setting.

Source/core/frame/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 49 matching lines @@
 
     // FIXME: This does not belong here.
     static void setMockScrollbarsEnabled(bool flag);
     static bool mockScrollbarsEnabled();
 
     // FIXME: naming_utilities.py isn't smart enough to handle OpenGL yet.
     // It could handle "GL", but that seems a bit overly broad.
     void setOpenGLMultisamplingEnabled(bool flag);
     bool openGLMultisamplingEnabled() { return m_openGLMultisamplingEnabled; }
 
+    void setAccessibilityEnabled(bool);
+    bool accessibilityEnabled() const { return m_accessibilityEnabled; }
+
     void setDelegate(SettingsDelegate*);
 
 private:
     Settings();
 
     void invalidate(SettingsDelegate::ChangeType);
 
     SettingsDelegate* m_delegate;
 
     GenericFontFamilySettings m_genericFontFamilySettings;
     bool m_openGLMultisamplingEnabled : 1;
     IntSize m_textAutosizingWindowSizeOverride;
     bool m_textAutosizingEnabled : 1;
+    bool m_accessibilityEnabled : 1;
 
     SETTINGS_MEMBER_VARIABLES
 };
 
 } // namespace blink
 
 #endif // Settings_h