Make durations look nice on the task list

appengine/swarming/elements/res/imp/tasklist/task-list-data.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:
 
     <bot-list-data>
 
@@ skipping 219 matching lines @@
           "_busy1", this.auth_headers, this.query_params);
       },
 
       _tasks: function() {
         if (!this._list || !this._list.items) {
           return [];
         }
         // Date.toString() looks like "Mon Aug 29 2016 09:03:41 GMT-0400 (EDT)"
         // we want to extract the time zone part and append it to the
         // locale time.
-        var str = (new Date()).toString();
+        var now = new Date();
+        var str = now.toString();
         var timeZone = str.substring(str.indexOf("("))
 
         // Do any preprocessing here
         this._list.items.forEach(function(t) {
           var tagMap = {};
           t.tags.forEach(function(tag) {
             var split = tag.split(":", 1)
             var key = split[0];
             var rest = tag.substring(key.length + 1);
             tagMap[key] = rest;
           });
           t.tagMap = tagMap;
           TIMES.forEach(function(time) {
             if (t[time]) {
-              var d = new Date(t[time]);
-              var locale = d.toLocaleString();
+              t[time] = new Date(t[time]);
+              var locale = t[time].toLocaleString();
               t["human_"+time] = locale + " " + timeZone;
             }
           });
+          // Running tasks have no duration set, so we can figure it out.
+          if (!t.duration && t.state === "RUNNING" && t.started_ts){
+            t.duration = (now - t.started_ts) / 1000;
+          }
+          // Make the duration human readable
+          if (t.duration){
+            t.human_duration = sk.human.strDuration(t.duration);
+          }
         });
         return this._list.items;
       }
     });
   })();
   </script>
 </dom-module>