Previously, benchpress would use `console.time()` and
`console.timeEnd()` to measure the start and end of a test in the
performance log. This used to work over navigations - if you called
`console.time(id)` then navigated to a different page, calling
`console.timeEnd(id)` would still insert an event in the performance
log.
As of Chrome 65, this is no longer the case. `console.timeEnd(id)` will
simply not insert an event in the performance log unless
`console.time(id)` was called on the same page. Likewise, using
`performance.measure()` does not work if the starting mark was on a
different page.
This simple workaround uses `performance.mark()` to insert events in the
performance log at the start and end of the test. Benchpress looks for
'-bpstart' and '-bpend' in the name of the performance mark, and
normalizes that to the start and end events expected by PerflogMetric
PR Close#24114
06d04002fd