Delay setting hidden until after isVisibleNow test.

Setting hidden prior to test guarantees the test will fail. This
then causes the exit animation to not be loaded and consequently
the window is immediately hidden. Then, when the window is removed
later it reappears in order to animate away. The consequent flash
is undesirable.

Bug: 7242373 fixed.
Change-Id: I56966bd9060124be372702090f86b29b4deea8c0