GitLab

Tweak the style of histograms/README.md and improve clarity.

Clarity changes:
- Improved the wording in the Directly Measure What You Want and
  Expired histogram notifier sections
- Removed "will" since the present tense is preferred
- Replaced some unclear expressions with clearer ones

Style changes:
- Periods are now consistently followed by one (not two) spaces
- Hyphens are replaced with em dashes where appropriate and spacing
  around them is corrected (no spaces)


Change-Id: I94e845fcf64e761814f7ae448ab1a50015238698
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2500141
Commit-Queue: Caitlin Fischer <caitlinfischer@google.com>
Reviewed-by: Jesse Doherty <jwd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#821316}