DOMUI prefs: Add and wire up a stub overlay for adding a startup page.

chrome/browser/resources/options/options_page.css

 #settings-title {
   height: 30px;
   -webkit-padding-end: 15px;
   padding-top: 20px;
   text-align: end;
   font-size: 140%;
   color: #c7c7c7;
 }
 
 #main-content {
@@ skipping 18 matching lines @@
 
 #close-overlay {
   float: right;
   position: relative;
   right: -20px;
   top: -20px;
   width: 20px;
   height: 20px;
 }
 
+#overlayview .button-strip {
+  text-align: end;
+}
+
 #overlayview {
   background: white;
   border-radius: 5px;
   padding: 30px;
 }
 
 #navbar-container {
   background: -webkit-gradient(linear,
                                left top,
                                left bottom,
@@ skipping 82 matching lines @@
   -webkit-margin-start: 18px;
 }
 
 .hidden {
   display: none;
 }
 
 .touch-slider {
   -webkit-appearance: slider-horizontal;
 }