Show bootstrap and server bot_code version

appengine/swarming/elements/res/imp/index/swarming-index.html

 <!--
   Copyright 2016 The LUCI Authors. All rights reserved.
   Use of this source code is governed under the Apache License, Version 2.0
   that can be found in the LICENSE file.
 
   This in an HTML Import-able file that contains the definition
   of the following elements:
 
     <swarming-index>
 
@@ skipping 29 matching lines @@
         margin-top: 10px;
         white-space: pre-wrap;
         background-color: #f5f5f5;
         border: 1px solid #ccc;
         border-radius: 4px;
       }
     </style>
 
     <swarming-app
       client_id="[[client_id]]"
-      auth_headers="{{auth_headers}}"
+      auth_headers="{{_auth_headers}}"
       permissions="{{_permissions}}"
       server_version="{{_server_version}}"
       name="Swarming Server"
       busy="[[_busy]]">
 
       <h2>Service Status</h2>
       <div>Server Version: [[_server_version.server_version]]</div>
+      <div>Bot Version: [[_server_version.bot_version]]</div>
       <ul>
         <li>
           <!-- TODO(kjlubick) convert these linked pages to Polymer-->
           <a href="/stats">Usage statistics</a>
         </li>
         <li>
           <a href="/restricted/mapreduce/status">Map Reduce Jobs</a>
         </li>
         <li>
           <a href$="[[_makeInstancesUrl(_server_version,_project_id)]]">View version's instances on Cloud Console</a>
@@ skipping 57 matching lines @@
 
       behaviors: [
           SwarmingBehaviors.CommonBehavior,
       ],
 
       properties: {
         client_id: {
           type: String,
         },
 
+
+        _auth_headers: {
+          type: String,
+        },
         _bootstrap_token: {
           type: String,
-          // TODO(kjlubick): fetch this from an API
-          value: "abc123",
+          value: "...",
         },
         _busy: {
           type: Boolean,
           value: false,
         },
         _host_url: {
           type: String,
           value: function() {
             return location.origin;
           },
         },
         _permissions: {
           type: Object,
         },
         _project_id: {
           type: String,
           value: function() {
             var idx = location.hostname.indexOf(".appspot.com");
             return location.hostname.substring(0, idx);
           },
         },
         _server_version: {
           type: Object,
         },
       },
 
+      observers: ["_fetchBootstrap(_permissions,_auth_headers)"],
+
 
       _cannotBootstrap: function(permissions) {
         return !(permissions && permissions.get_bootstrap_token);
       },
 
+      _fetchBootstrap: function(permissions, auth_headers) {
+        if (!auth_headers || !permissions || this._cannotBootstrap(permissions)) {
+          return;
+        }
+        this.set("_busy", true);
+
+        sk.request("POST", "/_ah/api/swarming/v1/server/token", undefined, auth_headers).then(JSON.parse).then(function(t) {
+          this.set("_bootstrap_token", t.bootstrap_token);
+          this.set("_busy", false);
+        }.bind(this)).catch(function(reason) {
+          console.log("Could not get token", reason);
+          this.set("_busy", false);
+        }.bind(this));
+      },
+
       _makeInstancesUrl: function(details, project_id) {
         return "https://console.cloud.google.com/appengine/instances?project="+
             project_id+"&versionId="+details.server_version;
       },
 
       _makeErrorUrl: function(project_id) {
         return "https://console.cloud.google.com/errors?project="+
             project_id;
       },
 
       _makeLogUrl: function(project_id) {
         return "https://pantheon.corp.google.com/logs/viewer?filters=text:status:500..599&project="+
             project_id;
       },
 
     });
   </script>
 </dom-module>