- Implement Platform.packageRoot and Platform.packageConfig based

sdk/lib/io/platform.dart

Index: sdk/lib/io/platform.dart
diff --git a/sdk/lib/io/platform.dart b/sdk/lib/io/platform.dart
index c9e1cc66d6d084212d356c0be7a099731327d3ce..7cd20a101000eb2cfc021aff6079ba6ac99b06ad 100644
--- a/sdk/lib/io/platform.dart
+++ b/sdk/lib/io/platform.dart
@@ -185,10 +185,19 @@ class Platform {
    * 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.
    *