MD Settings: add a <controlled-button> that uses prefs to disable itself

chrome/browser/resources/settings/controls/controlled_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-button',
+
+  behaviors: [CrPolicyPrefBehavior, PrefControlBehavior],
+
+  properties: {
+    disabled: {
+      type: Boolean,
+      computed: 'computeDisabled_(pref)',
+      reflectToAttribute: true,
+    },
+  },
+
+  /**
+   * @param {!chrome.settingsPrivate.PrefObject} pref
+   * @return {boolean} Whether the button is controlled.
+   * @private
+   */
+  computeDisabled_: function(pref) {
+    return this.isPrefPolicyControlled(pref);
+  },
+
+  /**
+   * @param {!Event} e
+   * @private
+   */
+  onIndicatorTap_: function(e) {
+    // :host([disabled]) applies pointer-events: none;, but we want mouse hover
+    // on indicators to work. So we selectively re-enable pointer-events on just
+    // the indicator, but disallow taps and clicks from triggering any on-tap on
+    // the host itself (i.e. <controlled-button on-tap="...">).
+    e.preventDefault();
+    e.stopPropagation();
+  },
+});