net/http: drop custom tls.Config cloning code.

Now that we have the Clone method on tls.Config, net/http doesn't need
any custom functions to do that any more.

Change-Id: Ib60707d37f1a7f9a7d7723045f83e59eceffd026
Reviewed-on: https://go-review.googlesource.com/31595
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

common.go

@@ -455,9 +455,13 @@ func ticketKeyFromBytes(b [32]byte) (key ticketKey) {
 	return key
 }
 
-// Clone returns a shallow clone of c.
-// Only the exported fields are copied.
+// Clone returns a shallow clone of c. It is safe to clone a Config that is
+// being used concurrently by a TLS client or server.
 func (c *Config) Clone() *Config {
+	// Running serverInit ensures that it's safe to read
+	// SessionTicketsDisabled.
+	c.serverInitOnce.Do(c.serverInit)
+
 	var sessionTicketKeys []ticketKey
 	c.mutex.RLock()
 	sessionTicketKeys = c.sessionTicketKeys

tls_test.go

@@ -508,6 +508,10 @@ func TestClone(t *testing.T) {
 	}
 
 	c2 := c1.Clone()
+	// DeepEqual also compares unexported fields, thus c2 needs to have run
+	// serverInit in order to be DeepEqual to c1. Cloning it and discarding
+	// the result is sufficient.
+	c2.Clone()
 
 	if !reflect.DeepEqual(&c1, c2) {
 		t.Errorf("clone failed to copy a field")