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This CL adds a Finch feature to show a "Suspicious site" Safety Tip
when there is a Safe Browsing delayed warning, i.e. when a page is
known to be malicious but Chrome is delaying the Safe Browsing warning
until user interaction.

This will allow us to measure 2 things:
- How a Safety Tip influences user behavior on known-bad sites
- How omnibox UI treatments influence user behavior when there is
  something (a Safety Tip) drawing their attention to the omnibox

This is implemented by checking if a delayed warning is present (and
the relevant Finch feature is enabled) inside
ReputationService::GetReputationStatusWithEngagedSites().

There's a bit of trickiness with the Finch features. Delayed warning
Safety Tips are controlled with their own separate Finch feature, so
that they can be controlled independently of the regular Safety Tips
feature. This is so that we can have simultaneous experiments where
one enables regular Safety Tips and another enables delayed warning
Safety Tips. (We aren't allowed to run multiple simultaneous
experiments that both enable the same feature.) Running simultaneous
experiments like this could mean that we end up with some users in
both experiments, but this should be rare, and even rarer still that a
user encounters both different types of Safety Tips (regular and
delayed warnings), so this shouldn't affect our metrics.

For convenience, I've reused the suspicious sites Safety Tips variant
-- both the UI and the SafetyTipStatus -- rather than introduce a new
type of Safety Tip. This seemed okay to me because we're not really
actively using/studying the suspicious site variant, so I figured we
can reuse it for this purpose. This does mean that we'll want to make
sure to turn off any existing Finch config for the suspicious site
Safety Tip before we run delayed warnings Safety Tip experiments.

Bug: 1146471
Change-Id: Ie98a12d0f95b1e4313493697d218385edb58212a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2523674Reviewed-by: Daniel Rubery <drubery@chromium.org>
Reviewed-by: Mustafa Emre Acer <meacer@chromium.org>
Reviewed-by: Joe DeBlasio <jdeblasio@chromium.org>
Commit-Queue: Emily Stark <estark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#825418}