Refactor Instant web UI (chrome://settings page).

chrome/browser/resources/options/pref_ui.js

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 cr.define('options', function() {
 
   var Preferences = options.Preferences;
 
   /**
    * Allows an element to be disabled for several reasons.
@@ skipping 80 matching lines @@
             else
               self.checked = Boolean(value);
 
             updateElementState_(self, event);
           });
 
       // Listen to user events.
       this.addEventListener(
           'change',
           function(e) {
+            if (self.customChangeHandler(e))
+              return;
             var value = self.inverted_pref ? !self.checked : self.checked;
             switch(self.valueType) {
               case 'number':
                 Preferences.setIntegerPref(self.pref,
                     Number(value), self.metric);
                 break;
               case 'boolean':
                 Preferences.setBooleanPref(self.pref,
                     value, self.metric);
                 break;
             }
           });
     },
 
     /**
      * Sets up options in checkbox element.
      * @param {String} valueType The preference type for this checkbox.
      */
     initializeValueType: function(valueType) {
       this.valueType = valueType || 'boolean';
     },
 
     /**
      * See |updateDisabledState_| above.
      */
     setDisabled: function(reason, disabled) {
       updateDisabledState_(this, reason, disabled);
     },
+
+    /**
+     * This method is called first while processing an onchange event. If it
+     * returns false, regular onchange processing continues (setting the
+     * associated pref, etc). If it returns true, the rest of the onchange is
+     * not performed. I.e., this works like stopPropagation or cancelBubble.
+     * @param {Event} event Change event.
+     */
+    customChangeHandler: function(event) {
+      return false;
+    },
   };
 
   /**
    * The preference name.
    * @type {string}
    */
   cr.defineProperty(PrefCheckbox, 'pref', cr.PropertyKind.ATTR);
 
   /**
    * Whether the preference is controlled by something else than the user's
@@ skipping 559 matching lines @@
     PrefNumber: PrefNumber,
     PrefNumeric: PrefNumeric,
     PrefRadio: PrefRadio,
     PrefRange: PrefRange,
     PrefSelect: PrefSelect,
     PrefTextField: PrefTextField,
     PrefButton: PrefButton
   };
 
 });