Linux sandbox: move CurrentProcessHasOpenDirectories

Move CurrentProcessHasOpenDirectories() to the Credentials class and rename
it to HasOpenDirectory().
Also add some unittests.

BUG=312380
R=jorgelo@chromium.org

Review URL: https://codereview.chromium.org/85403011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237242 0039d316-1c4b-4281-b951-d872f2087c98
4 files changed