Profile capybara request times
What
It is possible to use poltergeist's page.driver.network_traffic
method to determine where the browser is spending time in our test suite. I've put together a prototype in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/10682.
Why
We should know where time is spent during our tests. Inspired partly by https://gitlab.com/gitlab-org/gitlab-ce/issues/30196, which highlighted that we were spending significant amounts of test time on the log in page.