GitLab

In https://chromium-review.googlesource.com/#/c/267554/ we added a new
error code to ChromeOS update engine. This adds FilesystemVerifierError
to histograms.xml.

BUG=None
TEST=unit tests, pretty_print.py.
R=deymo@chromium.org

Review URL: https://codereview.chromium.org/1108843005

Cr-Commit-Position: refs/heads/master@{#327222}