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This patch relands the following CL:
https://chromium-review.googlesource.com/c/chromium/src/+/821090

This is a small refactor that should have some performance wins. Now
that PlzNavigate has launched, we should be dispatching our preconnects
after the initial navigation request has gone out, not before. This is
because frequently (especially on Android), dispatching preconnects
tends to hog the IO thread, delaying the initial request.

Note that this predictor is probably going away, but this CPU work
is in the critical path of some other work I am planning on tackling.

Bug: 792524
Change-Id: I03b058af249088f779dfb574c8552b32150bea2c
Reviewed-on: https://chromium-review.googlesource.com/826783Reviewed-by: Matt Menke <mmenke@chromium.org>
Commit-Queue: Charlie Harrison <csharrison@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524308}