Fix possible map::end() dereference in AppCacheUpdateJob triggered by a compromised renderer.

BUG=551044

Review URL: https://codereview.chromium.org/1418783005

Cr-Commit-Position: refs/heads/master@{#358815}
  void SwapCacheCallback(bool result, void* param) {
    last_swap_result_ = result;
    last_callback_param_ = param;
  }

  void SwapCacheCallback(bool result, void* param) {
    last_swap_result_ = result;
    last_callback_param_ = param;
  }
