Flakyness: fix notifications/ tests.

LayoutTests/http/tests/resources/permissions-helper.js

 // This file provides a PermissionsHelper object which can be used by
 // LayoutTests using testRunner to handle permissions. The methods in the object
 // return promises so can be used to write idiomatic, race-free code.
 //
 // The current available methods are:
 // - setPermission: given a permission name (known by testRunner) and a state,
 // it will set the permission to the specified state and resolve the promise
 // when done.
 // Example:
 // PermissionsHelper.setPermission('geolocation', 'prompt').then(runTest);
@@ skipping 30 matching lines @@
                 result.onchange = null;
                 resolver();
             };
 
             testRunner.setPermission(name, state, location.origin, location.origin);
         });
       });
     }
   }
 })();