Don't wait for windows which are goneForLayout

Gone for layout means that relayout won't be requested from
that window. This means that the sync engine would end up
waiting forever since there won't be a draw if there's no
layout.

Bug: 161980187
Test: everything works like normal, but later CLs don't get
      hung up here.
Change-Id: I96d5a68012a71ec27ede1168d03f5240244823aa