Changed look of pin keyboard.

chrome/browser/resources/chromeos/quick_unlock/pin_keyboard.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: '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 erase the last character of the entered
+  // PIN value.
+  onPinClear_: function() {
+    var pin = this.$$('#pin-input');
+    pin.value = pin.value.substring(0, pin.value.length - 1);
+  },
+
   // Called when the user wants to submit the PIN.
   onPinSubmit_: function() {
     var pin = this.$$('#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.
     if (event.keyCode == 13) {
       this.onPinSubmit_();
       event.preventDefault();
     }
   }
 });