func (tlsHandshakeTimeoutError) Error() string   { return "net/http: TLS handshake timeout" }

// fakeLocker is a sync.Locker which does nothing. It's used to guard
// test-only fields when not under test, to avoid runtime atomic
// overhead.
type fakeLocker struct{}

func (fakeLocker) Lock()   {}
func (fakeLocker) Unlock() {}

// cloneTLSConfig returns a shallow clone of cfg, or a new zero tls.Config if