Changes

ss: replace granularity with checkpoint attribute and add synchronization

This patch creates an interal state for the pss. The state keeps track
of which checkpoint it is in. This process was initially put forth by
Matthew Khouzam, Fabien Reumont-Locke improved it.

We are also adding a synchronization on the methods that modify
the trasState to avoid a race condition.

Signed-off-by: Abdellah Rahmani <rahmaniabdellah1994@gmail.com>
Change-Id: I9af752ae154fceb1c31ed57b64f0c17650c55703