Add settings UI for managing defaults

chrome/browser/resources/options2/web_intents_defaults.css

+/* Copyright (c) 2012 The Chromium Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file. */
+
+#services-list > div.deletable-item {
+  /* override the fixed 32px height of standard row. */
+  height: auto;
+}
+
+.intents-column-headers {
+  display: -webkit-box;
+  font-size: 13px;
+  font-weight: bold;
+}
+
+.intents-row {
+  margin: 5px;
+}
+
+.intents-preferred-service {
+  font-weight: bold;
+}
+
+.intents-service-matching-criteria {
+  color: #555;
+  font-size: .85em;
+}
+
+.intents-remove-column {
+  -webkit-box-flex: 1;
+}
+
+div > .intents-remove-column {
+  opacity: 0;
+}
+
+div:not(.none):hover > .intents-remove-column {
+  opacity: 1;
+}
+
+#intents {
+  min-height: 250px;
+}