Freeze task bounds when relaunching

To make sure that task is only laid out with the size
that matches the current configuration, we have to "freeze"
the task bounds when we send a configuration change. Without this
change, it could happen that the app already laid out with the new
task bounds, but still had the old configuration, leading to
wrong layouts.

Bug: 26311778
Bug: 25015474

Change-Id: I8d3a3fdf3735f446a4affbbdb4986dafc97623a5