Pin keyboard use enter to submit when focus is not on a button.

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.
 
 /**
  * @fileoverview
  * 'pin-keyboard' is a keyboard that can be used to enter PINs or more generally
  * numeric values.
  *
  * Properties:
@@ skipping 17 matching lines @@
   properties: {
     /** The value stored in the keyboard's input element. */
     value: {
       type: String,
       notify: true,
       value: '',
       observer: 'onPinValueChange_'
     }
   },
 
+  // The current focused element.
+  focusedElement_: undefined,
+
   /** Transfers focus to the input element. */
   focus: function() {
-    this.$$('#pin-input').focus();
+    var pinInput = this.$$('#pin-input');
+    pinInput.focus();
+    this.focusedElement_ = pinInput;
+  },
+
+  /** Called when a pin keyboard has a key pressed. */
+  onButtonKeyUp_: function(event, detail) {
+    // Only if tab has been pressed do we want change the focus.
+    if (event.target.receivedFocusFromKeyboard)
+      this.focusedElement_ = event.target;
   },
 
   /** Called when a keypad number has been tapped. */
   onNumberTap_: function(event, detail) {
     var numberValue = event.target.getAttribute('value');
     this.value += numberValue;
+
+    // If the tabbed element is clicked we want to keep the focus, otherwise
+    // transfer focus to the input.
+    if (this.focusedElement_ != event.target)
+      this.focus();

[jdufault, 2016/07/06 19:07:05]

Can this just be

  // Only focus buttons if the user tabbed to them.
  if (!event.target.receivedFocusFromKeyboard)
    this.focus()

If that works, then all the other changes can be reverted.

   },
 
   /** Fires a submit event with the current PIN value. */
   firePinSubmitEvent_: function() {
     this.fire('submit', { pin: this.value });
   },
 
   /**
    * Fires an update event with the current PIN value. The event will only be
    * fired if the PIN value has actually changed.
@@ skipping 30 matching lines @@
   },
 
   /**
    * Changes the color of the submit button if PIN is ready.
    * @param {string} value
    */
   computeSubmitClass_: function(value) {
     return value.length > 0 ? 'ready-background' : '';
   }
 });