Specifically:
- Include the raw value of Chrome's "ap" and cohort "name" values in
  crash keys -- these are the magic values by which Chrome determines
  which update channel it is on. Having the values in crash keys will
  give us data to confirm that the channel identification logic is
  correct.
- Include the cohort "name" value in about:version for convenient
  access.

BUG=579504

Review-Url: https://codereview.chromium.org/2797433002
Cr-Commit-Position: refs/heads/master@{#462018}