SF: Do not trace FrameTimeline before start

Filter FrameTimeline events for frames started before the trace started.

Bug: 364194637
Test: manual
Flag: com.android.graphics.surfaceflinger.flags.filter_frames_before_trace_starts
Change-Id: I9185f384f306eddab1afc2ea9d7901dd70d2f1a2
6 files changed