NTP/History: Remove comments referring to flexbox bug.

chrome/browser/resources/history/history.css

 /* 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. */
 
 html[dir=rtl] body.uber-frame > .page {
   -webkit-margin-end: 0;
 }
 
 #top-container {
   margin-top: 16px;
@@ skipping 423 matching lines @@
 .entry .title > a:hover {
   text-decoration: underline;
 }
 
 .fade-out {
   -webkit-transition: opacity 200ms;
   opacity: 0;
 }
 
 button.menu-button.drop-down {
-  /* Workaround for bug in flex box: http://crbug.com/223542 */
   min-width: 12px;
   top: 0;
 }
 
 #action-menu > :not(hr) {
   line-height: 29px;
   outline: none;
 }
 
 body:not(.has-results) #results-pagination {
@@ skipping 32 matching lines @@
 }
 
 /* Clear the float to ensure that #results-pagination encloses its children. */
 #results-pagination::after {
   clear: both;
   content: '';
   display: block;
   height: 0;
   visibility: hidden;
 }