When adding a window evaluate all tasks.

Previously the code was adding a window based only on the tasks on
the stack belonging to the window being added. But if a window from
another stack was on top the window would be added out of order.

In particular when there was a dialog over the launcher app and the
device was rotated, the launcher window was being added over the
dialog. This caused the launcher icons to obscure the dialog and for
the dialog buttons to be untouchable.

Fixes bug 9984067.

Change-Id: I9a57eb641d118f4a90e98af8ca77127ab5364e79