Linux: add basic unprivileged namespace support.

The Credentials class now has basic support for unprivileged namespaces.

BUG=312380
R=jorgelo@chromium.org

Review URL: https://codereview.chromium.org/54643010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233041 0039d316-1c4b-4281-b951-d872f2087c98
4 files changed