net/http/httputil: don't leak goroutines in DumpRequestOut

Fixes #7869

LGTM=dsymonds
R=golang-codereviews
CC=adg, dsymonds, golang-codereviews, rsc
https://golang.org/cl/91770048

src/pkg/net/http/httputil/dump.go

@@ -107,6 +107,7 @@ func DumpRequestOut(req *http.Request, body bool) ([]byte, error) {
 			return &dumpConn{io.MultiWriter(&buf, pw), dr}, nil
 		},
 	}
+	defer t.CloseIdleConnections()
 
 	_, err := t.RoundTrip(reqSend)
 

src/pkg/net/http/httputil/dump_test.go

@@ -11,6 +11,7 @@ import (
 	"io/ioutil"
 	"net/http"
 	"net/url"
+	"runtime"
 	"strings"
 	"testing"
 )
@@ -113,6 +114,7 @@ var dumpTests = []dumpTest{
 }
 
 func TestDumpRequest(t *testing.T) {
+	numg0 := runtime.NumGoroutine()
 	for i, tt := range dumpTests {
 		setBody := func() {
 			if tt.Body == nil {
@@ -156,6 +158,9 @@ func TestDumpRequest(t *testing.T) {
 			}
 		}
 	}
+	if dg := runtime.NumGoroutine() - numg0; dg > 4 {
+		t.Errorf("Unexpectedly large number of new goroutines: %d new", dg)
+	}
 }
 
 func chunk(s string) string {