Add PID to report_sample.py

This is equivalent to the output of running `perf script -F +pid`

This field is read by Firefox Profiler to group tids by their process:  https://profiler.firefox.com/docs/#/./guide-perf-profiling?id=step-2-convert-the-profile

Change-Id: I5002110cb76ad76941fb9ee19755e5c1bafdfae3
BUG=198242250
1 file changed