Minor CSS cleanup.

chrome/browser/resources/options/options_page.css

+.hbox {
+  display: -webkit-box;
+  -webkit-box-orient: horizontal;
+}
+
+.vbox {
+  display: -webkit-box;
+  -webkit-box-orient: vertical;
+}
+
+.stretch {
+  -webkit-box-flex: 1;  
+}
+
 .frozen,
 .subpage-sheet-container.frozen {
   position: fixed;
 }
 
 #search-field {
   font-size: inherit;
   margin: 0;
 }
 
@@ skipping 557 matching lines @@
   display: table-cell;
   vertical-align: baseline;
   border-bottom: 1px solid #eeeeee;
 }
 
 /* do not display a border after the last section in the table */
 .displaytable:not([searching='true']) > section:last-child > *  {
   border-bottom: none;
 }