Changing command line flag from disable appcontainer to enable appcontainer. As there are some reports on stable channel which suggest that CreateProcess is randomly failing when used with lowbox token, changing disable appcontainer flag to enable if required.

BUG=467920
R=wfh@chromium.org, jschuh@chromium.org

Review URL: https://codereview.chromium.org/1258173002

Cr-Commit-Position: refs/heads/master@{#340815}
(cherry picked from commit 354d94497b96ffa913a7c5d562d2d88d658b9401)

Conflicts:
	content/common/sandbox_win.cc

Review URL: https://codereview.chromium.org/1263643003.

Cr-Commit-Position: refs/branch-heads/2403@{#582}
Cr-Branched-From: f54b8097a9c45ed4ad308133d49f05325d6c5070-refs/heads/master@{#330231}
3 files changed