Prevent adding an empty email option in the feedback app in guest mode

chrome/browser/resources/feedback/js/feedback.js

 // Copyright 2013 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.
 
 /**
  * @type {string}
  * @const
  */
 var SRT_DOWNLOAD_PAGE = 'https://www.google.com/chrome/cleanup-tool/';
 
@@ skipping 326 matching lines @@
         chrome.app.window.current().show();
 
         var screenshotDataUrl = screenshotCanvas.toDataURL('image/png');
         $('screenshot-image').src = screenshotDataUrl;
         $('screenshot-image').classList.toggle('wide-screen',
             $('screenshot-image').width > MAX_SCREENSHOT_WIDTH);
         feedbackInfo.screenshot = dataUrlToBlob(screenshotDataUrl);
       });
 
       chrome.feedbackPrivate.getUserEmail(function(email) {
+        // Never add an empty option.
+        if (!email)
+          return;
         var optionElement = document.createElement('option');
         optionElement.value = email;
         optionElement.text = email;
         optionElement.selected = true;
         // Make sure the "Report anonymously" option comes last.
         $('user-email-drop-down').insertBefore(optionElement,
             $('anonymous-user-option'));
       });
 
       // Initiate getting the system info.
@@ skipping 87 matching lines @@
     $('cancel-button').onclick = cancel;
     $('remove-attached-file').onclick = clearAttachedFile;
 // <if expr="chromeos">
     $('performance-info-checkbox').addEventListener(
         'change', performanceFeedbackChanged);
 // </if>
   });
 }
 
 initialize();