Fix the System Profile to not load extensions. It could otherwise be forced
to by GPO.
A few releases ago I introduced a System Profile to back the User Manager
(
https://codereview.chromium.org/847733005). This profile, however, is
causing some problems. I'm trying to reduce those by making clearer the
contract of what it's for: A profile that doesn't take a browser window,
has no extensions, writes little to disk, etc.
This certainly addresses issue #4 raised within the bug, and address the
other issues as well (I can't repro them). This CL generally hardens Chrome
for the System Profile in a lot of the same ways we do the Guest Profile.
BUG=482176