runtime/trace: implement user events #16619
Description
https://golang.org/s/go15trace specifies user events:
Runtime/pprof package also exposes a set of functions for emission of user events:
package pprof func TraceEvent(id string) func TraceScopeStart(id string) func TraceScopeEnd(id string)
But there is no implementation at this time.
Those would be invaluable to properly debug latency problems.
(According to @dvyukov there is no one actively working on it, so I might give it a try.)