GitLab

This CL makes WebappActivity use:
- TabModelImpl
- CustomTabTabPersistencePolicy instead of WebappDirectoryManager

BUG=1032291

Change-Id: I7adc8288105aa161eedbab4ba37724d91c305e07
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1965900
Commit-Queue: Peter Kotwicz <pkotwicz@chromium.org>
Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Reviewed-by: Peter Conn <peconn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#727021}