Better coordination of transition destination.

Bug 15470128
Bug 15470558

Wait for shared element destinations to be complete
before sending it to the calling activity.

Don't allow layout between setting final destination
and the transition values capture.

Use snapshots to hold the final position while waiting
for the called Activity to take the shared element.

Fixed problem with exiting views sometimes disappearing
when exiting.

Change-Id: Ibc655f7bb9e8dd6e8a15778c96931e3d845cc15c