DPCHECK known conditions when we guess false in CurrentProcessHasOpenDirectories

openat(AT_FDCWD, "/proc/self/fd", ...) can fail if we have been chrooted
(eg into /proc/self/fdinfo) without directory listing permissions on the
new root dir (hence EACCES).  And even if we did have this permission,
/proc wouldn't exist (hence ENOENT).

TEST=Make a debug build or a release build with dcheck_always_on=1 and verify that this DPCHECK does not fail.

BUG=314985

Review URL: https://codereview.chromium.org/59763014

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237766 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237766