Allow switching between extended and unified

chrome/browser/resources/options/chromeos/display_options.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. */
 
 #display-options-page {
   background-color: rgb(240, 240, 240);
 }
 
 #display-options-content-area {
   padding: 0;
@@ skipping 55 matching lines @@
 
 .selected-display-option-row {
   margin-top: 10px;
 }
 
 .selected-display-option-title {
   display: inline-block;
   margin-right: 10px;
 }
 
+.xxx {

[xiyuan, 2015/05/20 20:17:52]

Is this needed?

+  display: inline-block;
+}
+
 .displays-display {
   -webkit-user-select: none;
   background: rgb(240, 240, 240);
   border: solid 1px;
   box-sizing: border-box;
   font-weight: bold;
   position: absolute;
   text-align: center;
   z-index: 2;
 }
 
 .display-mirrored {
   border: solid 1px;
 }
 
 .displays-focused {
   border: solid 2px rgb(0, 138, 255);
   color: rgb(0, 138, 255);
 }
 
 #display-options-toggle-mirroring {
   margin-right: 5px;
 }
 
 .display-options-button {
   width: 130px;
 }
+
+.controlled-setting-with-label,

[xiyuan, 2015/05/20 20:17:51]

This line has side effect because it applies to all elements with
controlled-setting-with-label class. Do we need it?

+.display-options-toggle-unified-desktop-label {
+  display: inline-block;
+}