[Files.app] Fix small bug/typo in permutation in NavigationList

The permutation logic has been refined in r225918, but it contained small bug/typo. This patch fixes them.

BUG=none
TEST=manual
R=hirono@chromium.org

Review URL: https://codereview.chromium.org/25474002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226195 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226195