deflake TestNavigate
deflake TestNavigate

For some reason, this test fails about half the time on Travis, but I
can't get it to fail even after stress-testing hundreds of concurrent
runs.

It might be because Travis is on a much older version of Chrome. We'll
fix that soon, by having chromedp select a specific version of Chrome.

For now, make it more conservative, not assuming that a Location after a
Navigate isn't racy.

chromedp/chromedp,knq/chromedp,chromedp/chromedp,chromedp/chromedp,knq/chromedp,knq/chromedp