Add a readonly attribute to cr-input.

ui/webui/resources/cr_elements/cr_input/cr_input.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
  * 'cr-input' is a single-line text field for user input. It is a convenience
  * element composed of a 'paper-input-decorator' and a 'input is="core-input"'.
  *
  * Example:
@@ skipping 28 matching lines @@
     /**
      * Set to true to style the element as disabled.
      *
      * @attribute disabled
      * @type boolean
      * @default false
      */
     disabled: {value: false, reflect: true},
 
     /**
+     * Set to true to make the input read-only.
+     *
+     * @attribute readonly
+     * @type boolean
+     * @default false
+     */
+    readonly: {value: false, reflect: true},
+
+    /**
      * Set to true to mark the input as required.
      *
      * @attribute required
      * @type boolean
      * @default false
      */
     required: {value: false, reflect: true},
 
     /**
      * The current value of the input.
@@ skipping 60 matching lines @@
     else
       this.$.input.removeAttribute('pattern');
   },
 
   /** @override */
   ready: function() {
     this.$.events.forward(this.$.input, ['change']);
     this.patternChanged();
   },
 });