DOMUI Prefs: Add a subpage for startup page management.

chrome/browser/resources/options/browser_options_page.css

-#startupPageManagement {
+#startupPageManagement.fullView {
   border: 1px solid #d9d9d9;
   border-radius: 2px;
 }
 
-#startupPages {
+#startupPagesShortList {
   height: auto;
   padding-bottom: 1px;
 }
 
-#startupPageManagement > :last-child {
+#startupPageManagement.fullView > :last-child {
   border-top: 1px solid #d9d9d9;
   padding: 5px 10px;
 }
 
 #customHomePageGroup {
   display: -webkit-box;
   -webkit-box-orient: horizontal;
 }
 
 #customHomePageGroup > div {
@@ skipping 39 matching lines @@
 #instantConfirmText {
   font-family: inherit;
   white-space: pre-wrap;
   width: 500px;
 }
 
 #instantConfirmLearnMore {
   position: absolute;
   bottom: 18px;
 }