GitLab

In https://codereview.chromium.org/2835733002 the ReadHistogramValues
method now returns one value instead of 2, but its call in
UpdateHistogramEnum still expect 2 where the 2nd was ignored.

BUG=711205

Review-Url: https://codereview.chromium.org/2866573002
Cr-Commit-Position: refs/heads/master@{#469532}