GitLab

 - Move all incognito code to incognito_menu_view.cc
   (to avoid special casing for ChromeOS)
 - Add "Exit incognito" button
 - Re-enable browser tests

Bug: 995720
Change-Id: I55674e9192065d4a185b712af391a56fdc56095a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1859962Reviewed-by: David Roger <droger@chromium.org>
Commit-Queue: Thomas Tangl <tangltom@chromium.org>
Cr-Commit-Position: refs/heads/master@{#705544}