Cleanup Lookalike interstitial browser tests.

This is a cleanup CL to add a few missing, and simplify existing,
interstitial tests. It also includes a few unaddressed nits from earlier
CLs.

Bug: 927924
Change-Id: Iaa177d8dfc69d127b6ba2af5c8f508d5e5d8db83
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1497756
Commit-Queue: Joe DeBlasio <jdeblasio@chromium.org>
Auto-Submit: Joe DeBlasio <jdeblasio@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Reviewed-by: Mustafa Emre Acer <meacer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638286}

chrome/browser/ui/omnibox/alternate_nav_infobar_delegate.cc

@@ -76,6 +76,7 @@ GURL AlternateNavInfoBarDelegate::GetLinkURL() const {
 
 bool AlternateNavInfoBarDelegate::LinkClicked(
     WindowOpenDisposition disposition) {
+  DCHECK(match_);
   history::HistoryService* const history_service =
       HistoryServiceFactory::GetForProfile(profile_,
                                            ServiceAccessType::IMPLICIT_ACCESS);