Add read-only environment variable access.

tests/standalone/src/io/PlatformTest.dart

Index: tests/standalone/src/io/PlatformTest.dart
diff --git a/tests/standalone/src/io/PlatformTest.dart b/tests/standalone/src/io/PlatformTest.dart
index 276a11ca5a3ee4b68c09803ff49ceaebb95f5ae0..334a5c8afadba2ee98b1a06b25ca8af348827a5e 100644
--- a/tests/standalone/src/io/PlatformTest.dart
+++ b/tests/standalone/src/io/PlatformTest.dart
@@ -1,4 +1,4 @@
-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2012, 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.
 
@@ -13,4 +13,6 @@ main() {
   Expect.isTrue(sep == '/' || (os == 'windows' && sep == '\\'));
   var hostname = p.localHostname();
   Expect.isTrue(hostname is String && hostname != "");
+  var environment = p.environment();
+  Expect.isTrue(environment is Map<String, String>);
 }