R1:059920c2dac5

Convert AphrontErrorView to safe HTML

Summary: Done by searching for `AphrontErrorView` and then `appendChild()`.

Test Plan:
Looked at Commit Detail.
Looked at Revision Detail.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2432

Differential Revision: https://secure.phabricator.com/D4843