feat(apm): Update Span timing from absolute ref (#2479)
feat(apm): Update Span timing from absolute ref (#2479)

Use performance.timeOrigin as the absolute reference to update Span
start and end timestamps.

Where performance.timeOrigin is not available, fallback to
performance.timing.navigationStart.
getsentry/raven-js,getsentry/raven-js,getsentry/raven-js,getsentry/raven-js