used to support the weird way Chrome manages processes, so doesn't belong
in the central CommandLine class.

This also provides an empty implementation on Mac & Windows to avoid some
ifdefs in the main functions.

TEST=everything compiles
BUG=none
Review URL: http://codereview.chromium.org/6002013

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@70276 0039d316-1c4b-4281-b951-d872f2087c98