Support drag&drop for startup pages

chrome/browser/resources/options/browser_options_page.css

 #startupPageManagement.settings-list > :last-child {
   border-top: 1px solid #d9d9d9;
   padding: 5px 10px;
 }
 
 #startupPagesList {
   min-height: 64px;
 }
 
 #startupPagesList .title {
   width: 40%;
 }
 
 #startupPagesList .url {
   -webkit-box-flex: 1;
   color: #666;
 }
 
+#startupPagesListDropmarker {
+  background-clip: padding-box;
+  background-color: hsl(214, 91%, 65%);
+  border-bottom-color: transparent;
+  border-radius: 0;
+  border-top-color: transparent;
+  border: 2px solid hsl(214, 91%, 65%);
+  box-sizing: border-box;
+  display: none;
+  height: 6px;
+  overflow: hidden;
+  pointer-events: none;
+  position: fixed;
+  z-index: 10;
+}
+
 #customHomePageGroup {
   display: -webkit-box;
   -webkit-box-orient: horizontal;
 }
 
 #customHomePageGroup > :last-child {
   -webkit-margin-start: 1ex;
   -webkit-box-flex: 1;
   position: relative;
 }
@@ skipping 37 matching lines @@
 #instantConfirmText {
   font-family: inherit;
   white-space: pre-wrap;
   width: 500px;
 }
 
 #instantConfirmLearnMore {
   position: absolute;
   bottom: 18px;
 }