Replace lookalike infobar with interstitial.

This CL replaces the lookalike URL infobar triggered in a
WebContentsObserver with a dedicated interstitial running in a
NavigationThrottle. Non-infobar-specific metrics are maintained, and
interstitial metrics are transitioned to the common
security_interstitials::metrics_helper. This CL also adds tests to
ensure bypassing the interstitial works properly.

Bug: 927924
Change-Id: I34209267e592e68739e2933dfc159c19d692f3c9
Reviewed-on: https://chromium-review.googlesource.com/c/1459337
Reviewed-by: Christopher Thompson <cthomp@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Reviewed-by: Mustafa Emre Acer <meacer@chromium.org>
Commit-Queue: Joe DeBlasio <jdeblasio@chromium.org>
Cr-Commit-Position: refs/heads/master@{#633931}
20 files changed