DOMUI: Don't show the close button on list items if the item is not selected.

chrome/browser/resources/options/options_page.css

 body {
   cursor: default;
   font-size: 100%;
 }
 
 a:link {
   color: rgb(63, 110, 194);
 }
 
 a:active {
@@ skipping 455 matching lines @@
   /* TODO(stuartmorgan): Replace with real images once they are available. */
   background-image: url("../../../app/theme/close_bar.png");
   border: none;
   display: block;
   height: 16px;
   opacity: 1;
   width: 16px;
 }
 
 list > *:not(:hover):not([lead]) .close-button,
+list > *:not(:hover):not([selected]) .close-button,
 list[disabled] .close-button,
 list .close-button[disabled] {
   opacity: 0;
   pointer-events: none;
 }
 
 list .close-button:hover {
   background-image: url("../../../app/theme/close_bar_h.png");
 }
 
@@ skipping 190 matching lines @@
 }
 
 html[os=mac] label > input[type=checkbox],
 html[os=mac] label > input[type=radio] {
   margin-top: 2px;
 }
 
 .suboption {
   -webkit-margin-start: 16px;
 }