- Implement Platform.packageRoot and Platform.packageConfig based

sdk/lib/io/platform.dart

 // 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.
 
 part of dart.io;
 
 /**
  * Information about the environment in which the current program is running.
  *
  * Platform provides information such as the operating system,
@@ skipping 167 matching lines @@
    * and the script name. Each fetch of executableArguments returns a new
    * List, containing the flags passed to the executable.
    */
   static List<String> get executableArguments => _Platform.executableArguments;
 
   /**
    * Returns the value of the --package-root flag passed to the executable
    * used to run the script in this isolate.  This is the directory in which
    * Dart packages are looked up.
    *
-   * If there is no --package-root flag, then the empty string is returned.
+   * If there is no --package-root flag, then null is returned.
    */
   static String get packageRoot => _Platform.packageRoot;
 
+/**
+ * Returns the value of the --packages flag passed to the executable
+ * used to run the script in this isolate.  This is the configuration which
+ * specifies how Dart packages are looked up.
+ *
+ * If there is no --packages flag, then the null is returned.
+ */
+  static String get packageConfig => _Platform.packageConfig;
+
   /**
    * Returns the version of the current Dart runtime.
    *
    * The returned `String` is formatted as the
    * [semver](http://semver.org) version string of the current dart
    * runtime, possibly followed by whitespace and other version and
    * build details.
    */
   static String get version => _version;
 }