Magnified frame not properly computed when keyguard goes away.

1. The keyguard force hides some windows when it is shown and as soon
   as the keyguard goes away there windows are made visible. However,
   the window transition that the keyguard is moving away is reported
   before the force hidden windows are shown which makes the screen
   magnifier compute the magnified region with an incomplete list of
   windows of interest.

bug:7215285

Change-Id: I3abc4d97b7a74de8183ad20477dadf66c82da037