Convert Lookalike URL throttle to use WillStartRequest.

This CL modifies the lookalike URL throttle to block requests before
they happen, rather than after they commit (but before Chrome processes
their response). This keeps logic cleaner (e.g. by not needing to worry
about remembering redirect chains across refreshed requests) at the
expense of possibly showing two interstitials in a row if the URL would
have triggered a different interstitial (as in invalid hostnames).

Bug: 941886
Change-Id: I0b9277b6880cc6c1bf247481ce208f7a42e52b9a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1526806
Commit-Queue: Joe DeBlasio <jdeblasio@chromium.org>
Reviewed-by: Mustafa Emre Acer <meacer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#642197}
3 files changed