Handle the 'cancel' case on attach a file.

chrome/browser/resources/feedback.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.
 
 // Constants.
 /** @const */ var FEEDBACK_LANDING_PAGE =
     'https://www.google.com/support/chrome/go/feedback_confirmation';
 /** @const */ var MAX_ATTACH_FILE_SIZE = 3 * 1024 * 1024;
 
 var selectedThumbnailDivId = '';
@@ skipping 77 matching lines @@
     return;
   $('screenshot-row').hidden = false;
 }
 
 /**
  * Reads the selected file when the user selects a file.
  * @param {event} evtFileSelected The on changed event for the file input box.
  */
 function onFileSelected(evtFileSelected) {
   var file = evtFileSelected.target.files[0];
+  if (!file) {
+    // User canceled file selection.
+    $('attach-file-checkbox').checked = false;
+    attachFileBinaryData = null;
+    return;
+  }
+
   if (file.size > MAX_ATTACH_FILE_SIZE) {
     $('attach-error').hidden = false;
 
     // Clear our selected file.
     $('attach-file').value = '';
     attachFileBinaryData = null;
     $('attach-file-checkbox').checked = false;
 
     return;
   }
@@ skipping 241 matching lines @@
   // Are screenshots disabled?
   if (!defaults.disableScreenshots)
     enableScreenshots();
 
   if (defaults.useSaved) {
     $('screenshot-link-tosaved').hidden = false;
   }
 }
 
 window.addEventListener('DOMContentLoaded', load);