Retain incognito state when tapping links on SadTab page

Bug: 737163
Change-Id: I49ea7f85e8f9a1854771995077e9f8e8c60cfad6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2815680


Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Reviewed-by: Tina Wang <tinazwang@chromium.org>
Reviewed-by: David Jean <djean@chromium.org>
Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Commit-Queue: Roger McFarlane <rogerm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#871963}