MD Settings: implement support for extension-controlled startup URLs

chrome/browser/resources/settings/controls/controlled_radio_button.js

 // Copyright 2016 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.
 
 Polymer({
   is: 'controlled-radio-button',
 
   behaviors: [CrPolicyPrefBehavior, PrefControlBehavior],
 
   properties: {
@@ skipping 12 matching lines @@
 
   listeners: {
     'focus': 'onFocus_',
   },
 
   /**
    * @return {boolean} Whether the button is disabled.
    * @private
    */
   computeControlled_: function() {
-    return this.isPrefPolicyControlled(assert(this.pref));
+    return this.pref.enforcement == chrome.settingsPrivate.Enforcement.ENFORCED;

[dpapad, 2016/11/18 23:46:28]

This is subtle. What is the difference between |pref.enforcement| and
|pref.policyEnforcement| which the  isPrefPolicyControlled refers to? Should we
just update |isPrefPolicyControlled| to look for both?

[Dan Beam, 2016/11/18 23:51:04]

the code you're looking at is outdated, there's only enforcement now

also, isPrefPolicyControlled() does exactly what it says: returns true if the
pref is POLICY controlled.  we need the radio group to be disabled if it's
POLICY controlled OR EXTENSION controlled.  they're not the same.

[dpapad, 2016/11/19 00:20:15]

Ok. I am slightly confused, so I am going to ask qustions to get a better
understanding.

Q1: CrPolicyPrefBehavior, is about POLICY controlled things only, and
PrefControlBehavior has nothing to do with prefs that are "controlled by"
(policy, extension, etc). Is my understanding accurate? If yes, isn't it
confusing if it has nothing to do with "controlled by" things?

Q2: Is this element using any of the CrPolicyPrefBehavior methods anymore? Or
can that behavior be removed?

[Dan Beam, 2016/11/19 00:50:05]

yes
yes
it's "control" as in a button or input.  we should rename it, along with
SettingsBooleanControlBehaviorImpl.
removed

   },
 
   /**
    * @param {boolean} controlled
    * @param {string} name
    * @param {chrome.settingsPrivate.PrefObject} pref
    * @return {boolean}
    * @private
    */
   showIndicator_: function(controlled, name, pref) {
     return controlled && name == Settings.PrefUtil.prefToString(pref);
   },
 
   /**
    * @param {!Event} e
    * @private
    */
   onIndicatorTap_: function(e) {
     // Disallow <controlled-radio-button on-tap="..."> when controlled.
     e.preventDefault();
     e.stopPropagation();
   },
 
   /** Focuses the internal radio button when the row is selected. */
   onFocus_: function() {
     this.$.radioButton.focus();
   },
 });