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

chrome/browser/resources/chromeos/quick_unlock/pin.js

Index: chrome/browser/resources/chromeos/quick_unlock/pin.js
diff --git a/chrome/browser/resources/chromeos/quick_unlock/pin.js b/chrome/browser/resources/chromeos/quick_unlock/pin.js
new file mode 100644
index 0000000000000000000000000000000000000000..49f3728095767de2ef465e711221e60430d5a5db
--- /dev/null
+++ b/chrome/browser/resources/chromeos/quick_unlock/pin.js
@@ -0,0 +1,36 @@
+// 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: 'pin-keyboard',
+
+  // Called when a keypad number has been tapped.
+  onNumberTap_: function(event, detail) {
+    var target = event.target;
+    var value = target.getAttribute('value');
+
+    var input = this.$$('#pin-input');
+    input.value += value;
+  },
+
+  // Called when the user wants to submit the PIN.
+  onPinSubmit_: function() {
+    var pin = this.$$('#pin-input').value;
+    this.fire('submit', { pin: pin });
+  },
+
+  // Called when a key event is pressed while the input element has focus.
+  onInputKeyDown_: function(event) {
+    // Up/down pressed, swallow the event to prevent the input value from
+    // being incremented or decremented.
+    if (event.keyCode == 38 || event.keyCode == 40)
+      event.preventDefault();
+
+    // enter pressed

[tommycli, 2016/05/04 19:29:03]

Enter pressed.

[jdufault, 2016/05/06 00:05:46]

Done.

+    if (event.keyCode == 13) {
+      this.onPinSubmit_();
+      event.preventDefault();
+    }
+  }
+});