Merge changes I9b4b0d4c,I1faca3aa,I38b538c1,I176c6641 into sc-dev

* changes:
  SF: do not skip validate if it is called more than a vsync earlier
  SF: region sampling scheduling optimization
  SF: return the expected wakeup time from VSyncDispatch
  SurfaceFlinger: previousFrameFence needs to check the current time