DevTools: migrate from ui-setting to settings extension point.

Source/devtools/front_end/ui/SettingsUI.js

 /*
  * Copyright (C) 2014 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 255 matching lines @@
     element.addEventListener("keydown", keyDownListener, false);
     function keyDownListener(event)
     {
         if (isEnterKey(event))
             eventListener(event);
     }
     return element;
 }
 
 /**
- * @constructor
+ * @interface
  */
-WebInspector.UISettingDelegate = function()
+WebInspector.SettingUI = function()
 {
 }
 
-WebInspector.UISettingDelegate.prototype = {
+WebInspector.SettingUI.prototype = {
     /**
      * @return {?Element}
      */
-    settingElement: function()
-    {
-        return null;
-    }
+    settingElement: function() { }
 }