GitLab

Miscellaneous fixes:

- Simplify the unit tests by unparameterizing them. Instead, the tests
  simply iterate over an array of test cases, using SCOPED_TRACE() to
  make it easier to debug failures.
- Convert metrics enums to be a scoped enumeration, which allows:
  - clang to enforce kMaxValue correctness
  - autodeduction of the max value by UMA_HISTOGRAM_ENUMERATION()
- Remove the unused Gamma enum. The metric itself was removed in
  https://crrev.com/c/1684563.

Bug: 742517, 1047547
Change-Id: I0a5b4aeaa8540505a7b0596a4d0df6f871fef8b3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2527341Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826393}