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

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

Index: chrome/browser/resources/settings/people_page/people_page.js
diff --git a/chrome/browser/resources/settings/people_page/people_page.js b/chrome/browser/resources/settings/people_page/people_page.js
index e00704a80c2104fca6eeb1a9444fbad05e7e86a0..f3a50f12ccb8f7d22aa30f4f14877554609e061d 100644
--- a/chrome/browser/resources/settings/people_page/people_page.js
+++ b/chrome/browser/resources/settings/people_page/people_page.js
@@ -63,6 +63,18 @@ Polymer({
     },
 
 <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,