Make the new index page more useful

appengine/swarming/elements/res/imp/tasklist/task-list.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:
 
     <task-list>
 
@@ skipping 266 matching lines @@
           def = "none";
         }
         var retVal = this._tag(task, col) || task[col] || [def];
         if (!Array.isArray(retVal)) {
           return [retVal];
         }
         return retVal;
       },
 
       _cannotCancel: function(task, permissions) {
-        return !(permissions && permissions.can_cancel_task &&
+        return !(permissions && permissions.cancel_task &&
               this._column("state", task) === "PENDING");
       },
 
       _cancelTask: function(e) {
         var task = e.model.task;
         if (!task || !task.task_id) {
           console.log("Missing task info", task);
           return
         }
         var id = task.task_id
@@ skipping 48 matching lines @@
         if (state === "RUNNING" || state === "PENDING") {
           return "pending";
         }
         return "";
       }
 
     });
   })();
   </script>
 </dom-module>