Add corelib tests

test/codegen/corelib/int_from_environment2_test.dart

Index: test/codegen/corelib/int_from_environment2_test.dart
diff --git a/test/codegen/corelib/int_from_environment2_test.dart b/test/codegen/corelib/int_from_environment2_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..2645337be5f69ce977c3c89aa29d643341fecd52
--- /dev/null
+++ b/test/codegen/corelib/int_from_environment2_test.dart
@@ -0,0 +1,15 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// 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.
+// SharedOptions=-Da=x -Db=- -Dc=0xg -Dd=+ -Dd=
+
+import "package:expect/expect.dart";
+
+main() {
+  Expect.isNull(const int.fromEnvironment('a'));
+  Expect.isNull(const int.fromEnvironment('b'));
+  Expect.isNull(const int.fromEnvironment('c'));
+  Expect.isNull(const int.fromEnvironment('d'));
+  Expect.isNull(const int.fromEnvironment('e'));
+}
+