p.m is accessed in WriteTo without holding p.mu.
Move the access inside the critical section.

The race detector catches this bug using this program:


package main

import (
	"os"
	"runtime/pprof"
	"time"
)

func main() {
	p := pprof.NewProfile("ABC")
	go func() {
		p.WriteTo(os.Stdout, 1)
		time.Sleep(time.Second)
	}()
	p.Add("abc", 0)
	time.Sleep(time.Second)
}


$ go run -race x.go 
==================
WARNING: DATA RACE
Write at 0x00c42007c240 by main goroutine:
  runtime.mapassign()
      /Users/josh/go/tip/src/runtime/hashmap.go:485 +0x0
  runtime/pprof.(*Profile).Add()
      /Users/josh/go/tip/src/runtime/pprof/pprof.go:281 +0x255
  main.main()
      /Users/josh/go/tip/src/p.go:15 +0x9d

Previous read at 0x00c42007c240 by goroutine 6:
  runtime/pprof.(*Profile).WriteTo()
      /Users/josh/go/tip/src/runtime/pprof/pprof.go:314 +0xc5
  main.main.func1()
      /Users/josh/go/tip/src/x.go:12 +0x69

Goroutine 6 (running) created at:
  main.main()
      /Users/josh/go/tip/src/x.go:11 +0x6e
==================
ABC profile: total 1
1 @ 0x110ccb4 0x111aeee 0x1055053 0x107f031

Found 1 data race(s)
exit status 66


(Exit status 66?)

Change-Id: I49d884dc3af9cce2209057a3448fe6bf50653523
Reviewed-on: https://go-review.googlesource.com/37730
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>