GitLab

Use enum to avoid meaningless decision like "kprefValue == 0" and
improve the readability.

Add an util class to help check the value of the incognito pref.

Change-Id: I005891908e261c8d292e2a861c7b5950a4f526d4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2586104Reviewed-by: Sergio Collazos <sczs@chromium.org>
Commit-Queue: Tina Wang <tinazwang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836644}