class Capybara::Window

def wait_for_stable_size(seconds = session.config.default_max_wait_time)
  res = yield if block_given?
  timer = Capybara::Helpers.timer(expire_in: seconds)
  loop do
    prev_size = size
    sleep 0.05
    return res if prev_size == size
    break if timer.expired?
  end
  raise Capybara::WindowError, "Window size not stable within #{seconds} seconds."
end