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.*)',
+    },
+  },
+
+  /**
+   * @param {!chrome.settingsPrivate.PrefObject} pref
+   * @return {boolean} Whether the button should be disabled.
+   * @private
+   */
+  computeDisabled_: function(pref) {
+    return this.isPrefPolicyControlled(pref);
+  },
+});