cros: Use runtime stylus detection for ash palette.

chrome/browser/resources/settings/device_page/device_page.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.
 
 /**
  * @fileoverview 'settings-device-page' is the settings page for device and
  * peripheral settings.
  */
 Polymer({
   is: 'settings-device-page',
 
   behaviors: [
     I18nBehavior,
     WebUIListenerBehavior,
     settings.RouteObserverBehavior,
   ],
 
   properties: {
     prefs: {
       type: Object,
       notify: true,
     },
 
     /**
-     * |hasMouse_| and |hasTouchpad_| start undefined so observers don't trigger
-     * until both have been populated.
+     * |hasMouse_|, |hasTouchpad_|, and |hasStylus_| start undefined so
+     * observers don't trigger until they have been populated.
      * @private
      */
     hasMouse_: Boolean,
 
     /** @private */
     hasTouchpad_: Boolean,
 
     /** @private */
-    stylusAllowed_: {
-      type: Boolean,
-      value: function() {
-        return loadTimeData.getBoolean('stylusAllowed');
-      },
-      readOnly: true,
-    },
+    hasStylus_: Boolean,

[stevenjb, 2017/02/03 23:11:26]

This should actually initialize to 'false', otherwise it will be undefined which
can have unexpected behavior (see https://github.com/Polymer/polymer/issues/2447
if you are curious). I believe that currently this will behave as expected, but
better I think to explicitly hide the section initially.

[jdufault, 2017/02/06 21:44:41]

Done; I was following the pattern for hasMouse_ and hasTouchpad_ so I've updated
those so they also explicitly initialize to false.

 
     /**
      * Whether power status and settings should be fetched and displayed.
      * @private
      */
     enablePowerSettings_: {
       type: Boolean,
       value: function() {
         return loadTimeData.getBoolean('enablePowerSettings');
       },
@@ skipping 50 matching lines @@
   ],
 
   /** @override */
   attached: function() {
     this.addWebUIListener(
         'has-mouse-changed', this.set.bind(this, 'hasMouse_'));
     this.addWebUIListener(
         'has-touchpad-changed', this.set.bind(this, 'hasTouchpad_'));
     settings.DevicePageBrowserProxyImpl.getInstance().initializePointers();
 
+    this.addWebUIListener(
+        'has-stylus-changed', this.set.bind(this, 'hasStylus_'));
+    settings.DevicePageBrowserProxyImpl.getInstance().initializeStylus();
+
     if (this.enablePowerSettings_) {
       this.addWebUIListener(
           'battery-status-changed', this.set.bind(this, 'batteryStatus_'));
       this.addWebUIListener(
           'power-sources-changed', this.powerSourcesChanged_.bind(this));
       settings.DevicePageBrowserProxyImpl.getInstance().updatePowerStatus();
     }
   },
 
   /**
@@ skipping 183 matching lines @@
    * @private
    */
   checkPointerSubpage_: function() {
     // Check that the properties have explicitly been set to false.
     if (this.hasMouse_ === false && this.hasTouchpad_ === false &&
         settings.getCurrentRoute() == settings.Route.POINTERS) {
       settings.navigateTo(settings.Route.DEVICE);
     }
   },
 });