Linux sandbox: cleanup BrokerProcess class.

A few style guide cleanups and more usage of scopers.

BUG=316486
R=rsesek@chromium.org

Review URL: https://codereview.chromium.org/84183002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236883 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236883