system-api: Add histogram warning to authpolicy ErrorType

Enum is being used in histograms.xml in Chromium.

BUG=chromium:676299
TEST=Just a comment change, what could possibly go wrong?!?

Change-Id: I9214a39a58ac54f9a4b8d2a37b3f1092eb5a81d2
Reviewed-on: https://chromium-review.googlesource.com/448516
Commit-Ready: Lutz Justen <ljusten@chromium.org>
Tested-by: Lutz Justen <ljusten@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Reviewed-by: Dan Erat <derat@chromium.org>
Reviewed-by: Roman Sorokin <rsorokin@chromium.org>
1 file changed