trace.go
func (t *trace) LazyPrintf(format string, a ...interface{}) {
	newfmt, newvals := addTrace(t, format, a...)
	Log.Printf(newfmt, newvals...)
	t.trace.LazyPrintf(format, a...)
}
func (t *trace) LazyPrintf(format string, a ...interface{}) {
	newfmt, newvals := addTrace(t, format, a...)
	Log.Printf(newfmt, newvals...)
	t.trace.LazyPrintf(format, a...)
}
// LazyPrintf evaluates its arguments with fmt.Sprintf each time the
// /debug/requests page is rendered. Any memory referenced by a will be
// pinned until the trace is finished and later discarded.