Add focus to directory after creating them via CreateDirFragment.

Since after createDiretoryFragment finishes, it's not synchronous that
the directory's view gets added, we need to wait for a layout pass so
recyclerView correctly updates itself with the new directory view. Once
then, we will request focus on the directory.

Bug: 27474438
Change-Id: Ib6087d63020265a837626b0dbcb511a9cd919285