Add read-only environment variable access.

runtime/bin/platform_impl.dart

Index: runtime/bin/platform_impl.dart
diff --git a/runtime/bin/platform_impl.dart b/runtime/bin/platform_impl.dart
index f859854e89cdeca9e3b20a6841ce45b30197b8ad..46f041370ee0ef805a63b622c6f300ffd2981a7f 100644
--- a/runtime/bin/platform_impl.dart
+++ b/runtime/bin/platform_impl.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.
 
@@ -9,6 +9,7 @@ class _Platform implements Platform {
   static String _pathSeparator() native "Platform_PathSeparator";
   static String _operatingSystem() native "Platform_OperatingSystem";
   static _localHostname() native "Platform_LocalHostname";
+  static _environment() native "Platform_Environment";
 
   int numberOfProcessors() {
     return _numberOfProcessors();
@@ -30,4 +31,19 @@ class _Platform implements Platform {
       return result;
     }
   }
+
+  Map<String, String> environment() {
+    var env = _environment();
+    if (env is OSError) {
+      throw env;
+    } else {
+      var result = new Map();
+      for (var str in env) {
+        var equalsIndex = str.indexOf('=');
+        assert(equalsIndex != -1);
+        result[str.substring(0, equalsIndex)] = str.substring(equalsIndex + 1);
+      }
+      return result;
+    }
+  }
 }