SF: handle presentTime in the past

presentTime in the past would result in Perfetto showing
unterminated slices. Fixing this issue by checking for this
case specifically, marking it janky, and fixing the presentTime to
be the endTime instead.

Test: SF unit tests
Bug: 271105399
Change-Id: I7e5d641dfe58717322b7a82b0609fc728e9a69fc