Add read-only environment variable access.

runtime/bin/platform_impl.dart

-// 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.
 
 class _Platform implements Platform {
   _Platform();
 
   static int _numberOfProcessors() native "Platform_NumberOfProcessors";
   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();
   }
 
   String pathSeparator() {
     return _pathSeparator();
   }
 
   String operatingSystem() {
     return _operatingSystem();
   }
 
   String localHostname() {
     var result = _localHostname();
     if (result is OSError) {
       throw result;
     } else {
       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;
+    }
+  }
 }