Add filter to task-list

appengine/swarming/elements/res/imp/common/swarming-app.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-app>
 
@@ skipping 95 matching lines @@
         },
         auth_headers: {
           type: Object,
           notify: true,
         },
         signed_in: {
           type: Boolean,
           value: false,
           notify:true,
         },
+        permissions: {
+          type: Object,
+          value: function() {
+            // TODO(kjlubick): Make this call the whoami endpoint after signing in.
+            return {
+              can_cancel_task: true,
+            }
+          },
+          notify: true,
+        },
 
         busy: {
           type: Boolean,
         },
         name: {
           type: String,
         },
       },
 
     });
   </script>
 </dom-module>
 
 <dom-module id="swarming-app-style">
   <style>
       * {
         font-family: sans-serif;
       }
       /* Only style anchor tags that are actually linking somewhere.*/
       a[href] {
         color: #1F78B4;
       }
   </style>
 </dom-module>