Allow loading other pages if current page is SSL interstitial.

Allow loading other pages if current page is SSL interstitial.

Before this change there was no way to load other pages (f.e. using
omnibox, or invoking history) if current page was SSL interstitial,
except after going back. The reason is that |clearTransientContentView|
was called after adding a pending nav item for the new site, as a result
pending item was discarded as a part of removing transient content view.

Marking nav item with bad SSL cert as Unsafe and calling
|clearTransientContentView| before adding a pending item causes removal
of 'unsafe' item as well as alows loading newly added pending item.

BUG=430090

Review URL: https://codereview.chromium.org/1291863004

Cr-Commit-Position: refs/heads/master@{#345330}