Work-In-Progress is a new change flag that can be set on
Gerrit changes. While a change is in WIP mode, certain things
are different:
* It doesn't send emails except to the change owner
* The "Reply" button becomes "Start Review"
* When a change is moved out of WIP, it sends a special
  "ready for review" message to any new reviewers
This is much more similar to the Rietveld model, where users
would "Publish" their changes for the reviewers to look at.

Bug: 721836
Change-Id: I3b9697e311fa176cb679ecefbfead9bb32b6afaf
Reviewed-on: https://chromium-review.googlesource.com/549015Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Reviewed-by: Quinten Yearsley <qyearsley@chromium.org>
Commit-Queue: Aaron Gable <agable@chromium.org>