AccessibilityNodeInfo reports no children for the topmost view in the tree.

1. My previous change to restrain AccessibilityNodeInfo to report children
   if it is root namespace did not take into account that the tompost view
   i.e. the decor view actually is a root namespace. Adding check to allow
   the info to report children of rthe topmost view but do not do so if a
   descendant is flagged as root namespace.

bug:5086988

Change-Id: Ib82b8ebe5a2c287ab1c5333d130ec50eb9ced78c