GitLab

This CL:
(1) Allows backward navigation on DontProceed if possible and there
is no suggested URL.
(2) Uses the button text 'Close page' instead of 'Back to safety'
in cases where the tab will be closed (no suggested URL and can't
go back).
(3) Records metrics when the interstitial is closed.
(4) Removes unused InterstitialParams reference, adds TODOs for
handling reloads/redirects and the DontProceed navigation, and
changes a function name for consistency.

Bug: 1058898
Change-Id: I5b017072a3b650cbf0479ab9df17ac91d9260a6a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2274250
Commit-Queue: Livvie Lin <livvielin@chromium.org>
Reviewed-by: Mustafa Emre Acer <meacer@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#785757}