Test that a deferred import of `dart:core` is ok.

tests/language/deferred_import_core_test.dart

Index: tests/language/deferred_import_core_test.dart
diff --git a/tests/language/type_variable_closure3_test.dart b/tests/language/deferred_import_core_test.dart
similarity index 51%
copy from tests/language/type_variable_closure3_test.dart
copy to tests/language/deferred_import_core_test.dart
index ecb1c39e82ed81cc01dd061dca2b5070890f985b..f3d66442b82fbf9e5e2166a71402a03664790d18 100644
--- a/tests/language/type_variable_closure3_test.dart
+++ b/tests/language/deferred_import_core_test.dart
@@ -2,17 +2,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import "package:expect/expect.dart";
+// Nothing in the language spec explicitly prohibits a deferred import of
+// 'dart:core'.  Make sure it doesn't lead to any strange behavior.
 
-class A<T> {}
-
-class C<T> {
-  a() {
-    return () => new A<T>();
-  }
-}
+import "dart:core" deferred as core;
 
 main() {
-  Expect.isTrue(new C<int>().a()() is A<int>);
-  Expect.isFalse(new C<int>().a()() is A<String>);
+  core.loadLibrary().then((_) => null);
 }