[Android] Test sign out dialog in AccountManagerFragment

Test two different sign-out flows in AccountManagerFragment.

When the user is signed in without sync consent, sign out dialog should
not be shown and data on device should not be wiped.

When the user is signed in with sync consent, sign out dialog should be
shown giving the user the choice to wipe device data.

Bug: 1138935
Change-Id: Ie31d14b8fac938614dda927076e81344d52d5774
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2478980
Reviewed-by: Marc Treib <treib@chromium.org>
Commit-Queue: Tanmoy Mollik <triploblastic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#820197}