Ship First Input Timing

Intent to ship:
https://groups.google.com/a/chromium.org/forum/?utm_medium=email&utm_source=footer#!msg/blink-dev/LN92hkaKCzw/Y-ryVxu5AgAJ

Bug: 823744, 841224
Change-Id: I1abf88264a61cb74df0eb40f6a77bdce14343d2b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1610256
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Reviewed-by: Nicolás Peña Moreno <npm@chromium.org>
Commit-Queue: Annie Sullivan <sullivan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661406}
6 files changed