Print Preview: Show error message if text is typed in Copies section

chrome/browser/resources/print_preview/data/ticket_items/copies.js

 // Copyright (c) 2012 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.
 
 cr.define('print_preview.ticket_items', function() {
   'use strict';
 
   /**
    * Copies ticket item whose value is a {@code string} that indicates how many
    * copies of the document should be printed. The ticket item is backed by a
    * string since the user can textually input the copies value.
    * @param {!print_preview.DestinationStore} destinationStore Destination store
    *     used determine if a destination has the copies capability.
    * @constructor
    * @extends {print_preview.ticket_items.TicketItem}
    */
   function Copies(destinationStore) {
     print_preview.ticket_items.TicketItem.call(
         this, null /*appState*/, null /*field*/, destinationStore);
   };
 
   Copies.prototype = {
     __proto__: print_preview.ticket_items.TicketItem.prototype,
 
     /** @override */
     wouldValueBeValid: function(value) {
-      if (/[^\d]+/.test(value)) {
-        return false;
-      }
-      var copies = parseInt(value, 10);
-      if (copies > 999 || copies < 1) {
-        return false;
-      }
-      return true;
+      return value != '';
     },
 
     /** @override */
     isCapabilityAvailable: function() {
       return !!this.getCopiesCapability_();
     },
 
     /** @return {number} The number of copies indicated by the ticket item. */
     getValueAsNumber: function() {
+      if (this.getValue() == '')

[dpapad, 2017/02/27 21:56:02]

Nit (optional)

var value = this.getValue();
return value == '' ? 0 : parseInt(value, 10);

[rbpotter, 2017/02/28 00:12:59]

Done.

+        return 0;
       return parseInt(this.getValue(), 10);
     },
 
     /** @override */
     getDefaultValueInternal: function() {
       var cap = this.getCopiesCapability_();
       return cap.hasOwnProperty('default') ? cap.default : '1';
     },
 
     /** @override */
@@ skipping 13 matching lines @@
               dest.capabilities.printer.copies) ||
              null;
     }
   };
 
   // Export
   return {
     Copies: Copies
   };
 });