net/http: add mechanism for marking flaky http tests

This shouldn't need to exist in general, but in practice I want something
like this a few times per year.

Change-Id: I9c220e58be44b7726f75d776f714212c570cf8bb
Reviewed-on: https://go-review.googlesource.com/18286Reviewed-by: Russ Cox <rsc@golang.org>

src/net/http/main_test.go

@@ -5,6 +5,7 @@
 package http_test
 
 import (
+	"flag"
 	"fmt"
 	"net/http"
 	"os"
@@ -15,6 +16,8 @@ import (
 	"time"
 )
 
+var flaky = flag.Bool("flaky", false, "run known-flaky tests too")
+
 func TestMain(m *testing.M) {
 	v := m.Run()
 	if v == 0 && goroutineLeaked() {
@@ -88,6 +91,12 @@ func setParallel(t *testing.T) {
 	}
 }
 
+func setFlaky(t *testing.T, issue int) {
+	if !*flaky {
+		t.Skipf("skipping known flaky test; see golang.org/issue/%d", issue)
+	}
+}
+
 func afterTest(t testing.TB) {
 	http.DefaultTransport.(*http.Transport).CloseIdleConnections()
 	if testing.Short() {

src/net/http/transport_test.go

@@ -1649,7 +1649,7 @@ func TestCancelRequestWithChannelBeforeDo(t *testing.T) {
 
 // Issue 11020. The returned error message should be errRequestCanceled
 func TestTransportCancelBeforeResponseHeaders(t *testing.T) {
-	t.Skip("Skipping flaky test; see Issue 11894")
+	setFlaky(t, 11894)
 	defer afterTest(t)
 
 	serverConnCh := make(chan net.Conn, 1)