Delete AXObjectCache when disabling accessibility setting.

Source/core/frame/Settings.h

Index: Source/core/frame/Settings.h
diff --git a/Source/core/frame/Settings.h b/Source/core/frame/Settings.h
index e4bf9d4cb3b41a84b8d5e8149a8d6425f907469f..538bc0457a2b1942b089ba0cc6828ab8c2e2ddb0 100644
--- a/Source/core/frame/Settings.h
+++ b/Source/core/frame/Settings.h
@@ -67,6 +67,9 @@ public:
     void setOpenGLMultisamplingEnabled(bool flag);
     bool openGLMultisamplingEnabled() { return m_openGLMultisamplingEnabled; }
 
+    void setAccessibilityEnabled(bool);
+    bool accessibilityEnabled() const { return m_accessibilityEnabled; }
+
     void setDelegate(SettingsDelegate*);
 
 private:
@@ -80,6 +83,7 @@ private:
     bool m_openGLMultisamplingEnabled : 1;
     IntSize m_textAutosizingWindowSizeOverride;
     bool m_textAutosizingEnabled : 1;
+    bool m_accessibilityEnabled : 1;
 
     SETTINGS_MEMBER_VARIABLES
 };