Experiment updating the UI strings to replace "incognito" to "private"

Launch bug: 863984

Bug: 865140
Change-Id: I1b67dd974d2eb5e15965d830c2fb304f8e9501a8
Reviewed-on: https://chromium-review.googlesource.com/1153837
Commit-Queue: Jian Li <jianli@chromium.org>
Reviewed-by: Ted Choc <tedchoc@chromium.org>
Reviewed-by: Dmitry Titov <dimich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579957}
16 files changed