Include child windows when looking for insertion point.

After finding a window in the window list we turn around and look in
the AppWindowToken.windows list for it. If it is a child of a window
in that list we should use the parent windows index as the search
result. Instead we gave up and ended up inserting the window at the
beginning of the windows list.

Bug 7357465 fixed.

Change-Id: If77f343b8597bfbb0b7fa41dedf7972d78d03020