Add histogram to differentiate token refresh errors.

This lets us look just at known-advanced-protection users, so we can
tell when there are real errors. This also lets us count those users.
Once this hits stable I'll setup Chirp alerts on this.  I also added
tests for metrics.

Bug: 919220
Change-Id: I44b0f17b129b565003fa58b43945034a949ca9c5
Reviewed-on: https://chromium-review.googlesource.com/c/1395835
Reviewed-by: Daniel Rubery <drubery@chromium.org>
Reviewed-by: Varun Khaneja <vakh@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Nathan Parker <nparker@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622089}
3 files changed