ntp4: disable animations for pages that are off screen

chrome/browser/resources/ntp4/new_tab.css

 /* Copyright (c) 2011 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.
  */
 
 html {
   font-family: segoe ui, arial, helvetica, sans-serif;
   font-size: 14px;
   /* It's necessary to put this here instead of in body in order to get the
      background-size of 100% to work properly */
@@ skipping 144 matching lines @@
 }
 
 #footer-content > * {
   margin: 0 9px;
 }
 
 #logo-img {
   margin-top: 4px;
 }
 
+.starting-up * {
+  -webkit-transition: none !important;
+}
+
 /* Trash. *********************************************************************/
 
 #trash {
   height: 100%;
   position: absolute;
   opacity: 0;
   right: 0;
   top: 50px;
   -webkit-transition: top 0.2s, opacity 0;
   -webkit-transition-delay: 0, 0.2s;
@@ skipping 34 matching lines @@
   min-width: 90px;
   opacity: 0.3;
   top: 0;
   z-index: 5;
   -webkit-transition: width 150ms, right 150ms, background-color 150ms;
 }
 
 .page-switcher:hover {
   background-color: rgba(0, 0, 0, 0.2);
 }