Don't crash if you call document.createText(null)

sky/tests/raw/null_text_crash.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:sky';
+import 'dart:sky' as sky;
+
 import '../resources/third_party/unittest/unittest.dart';
 import '../resources/unit.dart';
 
 void main() {
   initUnit();
 
-  test("color accessors should work", () {
-    Color foo = new Color(0x12345678);
-    expect(foo.alpha, equals(0x12));
-    expect(foo.red, equals(0x34));
-    expect(foo.green, equals(0x56));
-    expect(foo.blue, equals(0x78));
+  test("createText(null) shouldn't crash", () {
+    var doc = new sky.Document();
+    doc.createText(null);
   });
 }