Add 'system' to cros browsers.

BUG=319227
TEST=manual
NOTRY=True

Review URL: https://codereview.chromium.org/68113027

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@235317 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 235317