websocket: fix build

Change-Id: I414c02fb0178e3280e1df4c04f0cff528f5de341
Reviewed-on: https://go-review.googlesource.com/12910
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>

websocket/websocket_test.go

@@ -14,6 +14,7 @@ import (
 	"net/http/httptest"
 	"net/url"
 	"reflect"
+	"runtime"
 	"strings"
 	"sync"
 	"testing"