SF: Adding dynamic switching between 30 and 60 Hz in Scheduler.

Turn on frame skipping when 30Hz.
Record FPS in systrace: 24, 30, 60.

Results from paying youtube app:
file:///Users/akrulec/Desktop/scheduler_24_fps_trace.html
file:///Users/akrulec/Desktop/scheduler_30_fps_trace.html
file:///Users/akrulec/Desktop/scheduler_60_fps_trace.html

see go/surface-flinger-scheduler for more info.

Test: SF tests pass.
Change-Id: Ief8efbd5f16a74ed8f84906cb341a368118423a7