Add a very basic PIN UI implementation that is shared between lock and settings.

chrome/browser/resources/settings/people_page/people_page.js

 // Copyright 2015 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-people-page' is the settings page containing sign-in settings.
  *
  * Example:
  *
@@ skipping 45 matching lines @@
 
     /** @private {!settings.SyncBrowserProxyImpl} */
     syncBrowserProxy_: {
       type: Object,
       value: function() {
         return settings.SyncBrowserProxyImpl.getInstance();
       },
     },
 
 <if expr="chromeos">
+    /**
+     * True if Pin Unlock is allowed on this machine.
+     */
+    pinUnlockAllowed_: {
+      type: Boolean,
+      value: function() {
+        /* TODO(jdufault): Return a real value. */

[tommycli, 2016/05/02 16:11:27]

We should probably return the real value before this is ready for committing.
It's adding an item to the loadTimeData right?

Look at how easy_unlock_settings_hnadler.cc is implemented:
https://code.google.com/p/chromium/codesearch#chromium/src/chrome/browser/ui/...

Maybe this portion should wait for a separate CL?

[jdufault, 2016/05/03 19:21:58]

I think it makes sense to define this using a private API method call instead,
because then we won't have to write a separate handler for the options page as
well.

So with the private API, pinUnlockAllowed will be defined something like:

  QuickUnlockMode[] modes = chrome.quickUnlockPrivate.getAllowedModes()
  return modes.includes(QuickUnlockMode.PIN);

or maybe

   return chrome.quickUnlockPrivate.isAllowed()

depending on if we treat all quick unlock modes the same w.r.t. policy.

[tommycli, 2016/05/04 19:29:02]

Ah I forgot you were doing a private extension API. This query will be fast and
synchronous right? (So it won't introduce a UI flicker?)

+        return false;
+      },
+      readOnly: true,
+    },
+
     /** @private {!settings.EasyUnlockBrowserProxyImpl} */
     easyUnlockBrowserProxy_: {
       type: Object,
       value: function() {
         return settings.EasyUnlockBrowserProxyImpl.getInstance();
       },
     },
 
     /**
      * True if Easy Unlock is allowed on this machine.
@@ skipping 162 matching lines @@
 
   /**
    * @private
    * @return {boolean}
    */
   isAdvancedSyncSettingsVisible_: function(syncStatus) {
     return syncStatus && syncStatus.signedIn && !syncStatus.managed &&
            syncStatus.syncSystemEnabled;
   },
 });