Enable error pages for layout tests.

Currently, we remove error page navigation for layout tests, which means
that we have strangely divergent behavior in some edge cases. This patch
removes that special-casing and fixes up tests that depended on the edge
cases.

Review-Url: https://codereview.chromium.org/1920873002
Cr-Commit-Position: refs/heads/master@{#390625}
30 files changed