[cros] Change how we track momemt to emit login-prompt-visible signal.

chrome/browser/resources/chromeos/login/screen_error_message.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.
 
 /**
  * @fileoverview Offline message screen implementation.
  */
 
 cr.define('login', function() {
   // Screens that should have offline message overlay.
@@ skipping 225 matching lines @@
         if (!currentScreen.classList.contains('faded')) {
           currentScreen.classList.add('faded');
           currentScreen.addEventListener('webkitTransitionEnd',
             function f(e) {
               currentScreen.removeEventListener('webkitTransitionEnd', f);
               if (currentScreen.classList.contains('faded'))
                 currentScreen.classList.add('hidden');
             });
         }
         chrome.send('networkErrorShown');
+        // Report back error screen UI being painted.
+        window.webkitRequestAnimationFrame(function() {
+          chrome.send('loginVisible');
+        });
       } else {
         chrome.send('hideCaptivePortal');
 
         if (!offlineMessage.classList.contains('faded')) {
           console.log('Hide offline message. state=' + state +
                       ', network=' + network + ', reason=' + reason);
 
           offlineMessage.onBeforeHide();
 
           offlineMessage.classList.add('faded');
@@ skipping 83 matching lines @@
    * via template.
    */
   ErrorMessageScreen.updateLocalizedContent = function() {
     $('error-message').updateLocalizedContent_();
   };
 
   return {
     ErrorMessageScreen: ErrorMessageScreen
   };
 });