net: drop flakey TestDialFailPDLeak

TestDialFailPDLeak was created for testing runtime-integrated netwrok
poller stuff and used during Go 1.2 development cycle. Unfortunately
it's still flakey because it depends on MemStats of runtime, not
pollcache directly, and MemStats accounts and revises its own stats
occasionally.

For now the codepaths related to runtime-intergrated network poller
are pretty stable, so removing this test case never suffers us.

Fixes #6553.

LGTM=josharian, iant
R=iant, josharian
CC=golang-codereviews
https://golang.org/cl/98080043

src/pkg/net/dial_test.go

@@ -425,60 +425,6 @@ func numFD() int {
 	panic("numFDs not implemented on " + runtime.GOOS)
 }
 
-// Assert that a failed Dial attempt does not leak
-// runtime.PollDesc structures
-func TestDialFailPDLeak(t *testing.T) {
-	if testing.Short() {
-		t.Skip("skipping test in short mode")
-	}
-	if runtime.GOOS == "windows" && runtime.GOARCH == "386" {
-		// Just skip the test because it takes too long.
-		t.Skipf("skipping test on %q/%q", runtime.GOOS, runtime.GOARCH)
-	}
-
-	maxprocs := runtime.GOMAXPROCS(0)
-	loops := 10 + maxprocs
-	// 500 is enough to turn over the chunk of pollcache.
-	// See allocPollDesc in runtime/netpoll.goc.
-	const count = 500
-	var old runtime.MemStats // used by sysdelta
-	runtime.ReadMemStats(&old)
-	sysdelta := func() uint64 {
-		var new runtime.MemStats
-		runtime.ReadMemStats(&new)
-		delta := old.Sys - new.Sys
-		old = new
-		return delta
-	}
-	d := &Dialer{Timeout: time.Nanosecond} // don't bother TCP with handshaking
-	failcount := 0
-	for i := 0; i < loops; i++ {
-		var wg sync.WaitGroup
-		for i := 0; i < count; i++ {
-			wg.Add(1)
-			go func() {
-				defer wg.Done()
-				if c, err := d.Dial("tcp", "127.0.0.1:1"); err == nil {
-					t.Error("dial should not succeed")
-					c.Close()
-				}
-			}()
-		}
-		wg.Wait()
-		if t.Failed() {
-			t.FailNow()
-		}
-		if delta := sysdelta(); delta > 0 {
-			failcount++
-		}
-		// there are always some allocations on the first loop
-		if failcount > maxprocs+2 {
-			t.Error("detected possible memory leak in runtime")
-			t.FailNow()
-		}
-	}
-}
-
 func TestDialer(t *testing.T) {
 	ln, err := Listen("tcp4", "127.0.0.1:0")
 	if err != nil {