Camera: Address time drift in presentation time

Consecutive expected presentation times returned from VsyncEventData
may fall into the same Vsync interval due to time drift. Mitigate the
problem by sutracting 1/3 of Vsync frame interval from the expected
presentation time.

Also added a varialbe initilization.

Frame miss+drop rates in 3 min tests:
60fps: 0.3%
30fps: 0.3%
60/30 dynamic frame rate: 1.7%

Test: Inspect the frame miss/drop rate via trace
Bug: 226242194
Change-Id: I93ecaeb72cf4520e1752c6ec948895af753c140b