cros: Clean up screenlockPrivate plumbing.

chrome/browser/resources/login/user_pod_row.css

 /* Copyright 2014 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.
  *
  * This is the stylesheet used by user pods row of account picker UI.
  */
 
 podrow {
   /* Temporarily disabled because animation interferes with updating screen's
    size. */
@@ skipping 141 matching lines @@
   display: none;
   font-size: 14px;
   height: 40px;
   text-overflow: ellipsis;
 }
 
 .pod[auth-type='userClick'] .password-label {
   display: -webkit-box;
 }
 
-.custom-button {
+.custom-icon {
   -webkit-box-align: center;
-  background-color: rgba(0, 0, 0, 0);
-  background-image: none;
-  cursor: pointer;
-  display: -webkit-box;
+  background-position: center;
+  background-repeat: no-repeat;
   height: 40px;
-  margin: 0;
-  max-width: 40px;
-  min-height: 0;
-  min-width: 0;
-  padding: 0;
-}
-
-button.custom-button:focus:active,
-button.custom-button:focus:hover {
-  border: 1px solid transparent !important;
-}
-
-.custom-button img {
-  max-height: 100%;
-  max-width: 100%;
+  width: 40px;
 }
 
 .pod input[type='password'] {
   -webkit-transition: opacity linear 150ms;
   background: white;
   border: none;
   border-radius: 0; /* override widgets.css rule */
   box-sizing: border-box;
   display: none;
   height: 40px;
@@ skipping 410 matching lines @@
 .pod.public-account.expanded .name,
 .pod.public-account.expanded .learn-more {
   display: none;
 }
 
 .pod.public-account.expanded .side-pane-divider,
 .pod.public-account.expanded .side-pane-container,
 .pod.public-account.animating .side-pane-container {
   visibility: inherit;
 }