[signin] Reset DiceTabHelper to initial state when reusing signin tab

Bug: 791948
Change-Id: Ie8f9c43ace98082e86d1bfbe01bc3ffe58a01fd6
Reviewed-on: https://chromium-review.googlesource.com/808979
Commit-Queue: David Roger <droger@chromium.org>
Reviewed-by: Trent Apted <tapted@chromium.org>
Reviewed-by: Mihai Sardarescu <msarda@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522397}
5 files changed