chromite: Add app_shell staging flag.

Add a staging flag that tells deploy_chrome.py to install
the app_shell executable and app_shell.pak.

BUG=chromium:351965
TEST=manual: built chromeos-chrome in conjunction with an
     ebuild change that sets this flag and checked that the
     expected files were installed

Change-Id: I967a93237ea85d7bf2fa80a1a035fb4e01538c1d
Reviewed-on: https://chromium-review.googlesource.com/190312
Tested-by: Daniel Erat <derat@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Don Garrett <dgarrett@chromium.org>
Commit-Queue: Daniel Erat <derat@chromium.org>
1 file changed