Add the flag for the experiment to change "incognito" to "private"

Bug: 865140
Change-Id: Id58e74ea8cda672252b5f6abce911ce7d849ee3e
Reviewed-on: https://chromium-review.googlesource.com/1142448
Commit-Queue: Jian Li <jianli@chromium.org>
Reviewed-by: Dmitry Titov <dimich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577223}
7 files changed