ChromeOS: update alignment of user POD error bubble.

ui/login/bubble.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.
  *
  * Css based bubble.
  */
 
 .bubble {
   -webkit-transition: opacity 200ms ease-in-out;
   background: rgba(0, 0, 0, 0.8);
   border-radius: 2px;
   color: rgba(255, 255, 255, 0.87);
   box-shadow: 0 2px 4px rgba(0, 0, 0, 0.2);
   font-size: 12px;
   margin: 2px;
   max-width: 250px;
-  padding: 16px;
+  padding: 8px;
   position: absolute;
 }
 
+.error-message-bubble::before {
+  -webkit-mask-image: url(../../ui/webui/resources/images/warning.svg);
+  -webkit-mask-position: left top;
+  -webkit-mask-repeat: no-repeat;
+  -webkit-mask-size: 20px;
+  background-color: rgb(255,255,255);
+  content: '';
+  display: block;
+  height: 20px;
+  left: 8px;
+  position: absolute;
+  top: 8px;
+  width: 100%;

[xiyuan, 2016/11/03 16:54:40]

nit: can we use a fixed width, e.g. 20px ?

[Alexander Alekseev, 2016/11/03 22:15:30]

Done.

+}
+
 .error-message-bubble {
-  -webkit-padding-start: 30px;
-  background: url(chrome://theme/IDR_WARNING) left top no-repeat;
-  background-size: 24px;
+  -webkit-padding-start: 20px;
+}
+
+.bubble[match-width] .error-message-bubble {
+  -webkit-padding-start: unset;
+  padding-top: 20px;
+}
+
+.bubble a {
+  color: #7baaf7;
+  text-decoration: none;
 }
 
 .error-message-bubble-padding {
   margin-bottom: 10px;
 }
 
 html[dir=rtl] .error-message-bubble {
   background-position: right top;
 }