Ensure non-resizeable tasks not in multi-window mode

This CL refines e1fb953 to make sure a non-resizeable task with
undefined windowing mode won't be resolved in multi-window mode
even when its parent is.

Bug: 171672645
Test: atest TaskTests
Change-Id: I311f0f9bd9dbadaa134370faea8db937160ea44f
3 files changed