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At present, the NavigationEntry page type always reports
PAGE_TYPE_NORMAL for all committed entries, even if an
error page is currently showing. There is a need for a
mechanism to detect when an error page is showing in order
to prevent zooming in that case, so we modify the
navigation entry to correctly report error pages.

BUG=403268

Review URL: https://codereview.chromium.org/580133002

Cr-Commit-Position: refs/heads/master@{#296614}