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When switching tabs, report the time it takes for the browser to send
the request to the renderer to become visible.

BUG=858944

Change-Id: Id11569162c433a66f61a4fd8dc8ef8c8b2f70327
Reviewed-on: https://chromium-review.googlesource.com/1136217Reviewed-by: Robert Kaplow (slow) <rkaplow@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Sadrul Chowdhury <sadrul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575025}