Support passing an environment variable map to child processes.

tests/standalone/src/io/PrintEnv.dart

Index: tests/standalone/src/io/PrintEnv.dart
diff --git a/tests/standalone/src/io/PrintEnv.dart b/tests/standalone/src/io/PrintEnv.dart
new file mode 100644
index 0000000000000000000000000000000000000000..3b2e818c443f2b23850d45a432be9316bbc81995
--- /dev/null
+++ b/tests/standalone/src/io/PrintEnv.dart
@@ -0,0 +1,9 @@
+// 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.
+
+#import('dart:io');
+
+main() {
+  print(Platform.environment()[new Options().arguments[0]]);
+}