Change int.fromEnvironment in VM to use same code as int.parse.

tests/corelib/int_from_environment2_test.dart

Index: tests/corelib/int_from_environment2_test.dart
diff --git a/tests/corelib/int_from_environment2_test.dart b/tests/corelib/int_from_environment2_test.dart
index 8b14526921916594381f22ea7a974a55825b8630..2645337be5f69ce977c3c89aa29d643341fecd52 100644
--- a/tests/corelib/int_from_environment2_test.dart
+++ b/tests/corelib/int_from_environment2_test.dart
@@ -1,7 +1,7 @@
 // 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
+// SharedOptions=-Da=x -Db=- -Dc=0xg -Dd=+ -Dd=
 
 import "package:expect/expect.dart";
 
@@ -9,4 +9,7 @@ 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'));
 }
+