DOMUI Prefs: Add a deletable item list type, and use it for startup pages.

chrome/browser/resources/options/options_page.css

 body {
   -webkit-user-select: none;
   cursor: default;
   font-size: 100%;
 }
 
 #settings-title {
   -webkit-padding-end: 24px;
   color: #53637d;
   font-size: 200%;
@@ skipping 374 matching lines @@
 
 list > .heading {
   color: #666666;
 }
 
 list > .heading:hover {
   background-color: transparent;
   border-color: transparent;
 }
 
+list .deletable-item {
+  display: -webkit-box;
+}
+
+list .deletable-item > :first-child {
+  -webkit-box-flex: 1;
+}
+
+list .close-button {
+  background-color: transparent;
+  /* TODO(stuartmorgan): Replace with real images once they are available. */
+  background-image: url("../../../app/theme/close_bar.png");
+  border: none;
+  height: 16px;
+  width: 16px;
+}
+
+list > *:not(:hover) .close-button, list[disabled] .close-button {
+  display: none;
+}
+
+list .close-button:hover {
+  background-image: url("../../../app/theme/close_bar_h.png");
+}
+
+list .close-button:active {
+  background-image: url("../../../app/theme/close_bar_p.png");
+}
+
 .left-side-table {
   display: -webkit-box;
 }
 
 .left-side-table > div:first-child {
   -webkit-box-flex: 1;
 }
 
 .left-side-table > :last-child {
   -webkit-padding-start: 20px;
@@ skipping 13 matching lines @@
 
 .favicon-cell {
   -webkit-padding-start: 20px;
   background-position: left;
   background-repeat: no-repeat;
 }
 
 list .favicon-cell {
   -webkit-margin-start: 7px;
   -webkit-padding-start: 26px;
+  display: block;
+  text-overflow: ellipsis;
+  overflow: hidden;
+  white-space: nowrap;
 }
 
 html[dir=rtl] .favicon-cell {
   background-position: right;
 }
 
 html[enable-background-mode=false] #background-mode-section {
  display: none;
 }
 
@@ skipping 39 matching lines @@
 label.radio > span,
 .suboption {
   -webkit-margin-start: 16px;
   display: block;
 }
 
 html[os=mac] label.checkbox > input,
 html[os=mac] label.radio > input {
   margin-top: 2px;
 }