onactivate = function(e) {
  var result = {
    resolve_value: false,
    match_count_before: -1,
    match_count_after: -1,
    message: "claim_worker_1",
  };

  self.clients
    .matchAll()
    .then(function(matched) {
      // should be 0
      result.match_count_before = matched.length;
    })
    .then(function() {
      return self.clients.claim();
    })
    .then(function(ret) {
      result.resolve_value = ret;
      return self.clients.matchAll();
    })
    .then(function(matched) {
      // should be 2
      result.match_count_after = matched.length;
      for (i = 0; i < matched.length; i++) {
        matched[i].postMessage(result);
      }
      if (result.match_count_after !== 2) {
        dump("ERROR: claim_worker_1 failed to capture clients.\n");
      }
    });
};