SF: Allow privileged clients to create layers offscreen

If the caller is privileged and a new layer has a null parent,
the new layer will be added to root. When recreating layer
state, we create layers as a privileged client so we need to
specify if a layer need to be added offscreen.

Test: presubmit
Bug: 200284593
Change-Id: If07953b401020b115b0e364ff03ac65503bdc0ed