Fix black flash during rotation of -1 screen with GEL.

We need to make sure the custom content is adding synchronously
while the rest of the workspace is being created. If we wait
for it to be added in a separate run task, we see a black
flash during rotation.
Also rename a few methods and remove obsolete methods.

Bug: 11802691
Change-Id: I3f6500aa1fabe68cef59ad8c764877f954986a99