Add access to the isolate package-root/package-map in Platform.

sdk/lib/io/platform_impl.dart

Index: sdk/lib/io/platform_impl.dart
diff --git a/sdk/lib/io/platform_impl.dart b/sdk/lib/io/platform_impl.dart
index 6380e0d7c92f622495d3c9ca2149db2baafdfda9..addee0b6af2d92d96896266622f16bf055d66c27 100644
--- a/sdk/lib/io/platform_impl.dart
+++ b/sdk/lib/io/platform_impl.dart
@@ -21,7 +21,7 @@ class _Platform {
    * a non-empty name and a value separated by a '=' character.
    * The name does not contain a '=' character,
    * so the name is everything up to the first '=' character.
-   * Values are everything after the first '=' charcacter.
+   * Values are everything after the first '=' character.
    * A value may contain further '=' characters, and it may be empty.
    *
    * Returns an [OSError] if retrieving the environment fails.
@@ -29,13 +29,28 @@ class _Platform {
   external static _environment();
   external static List<String> _executableArguments();
   external static String _packageRoot();
+  external static _packageResolution();
   external static String _version();
 
   static String executable = _executable();
   static String resolvedExecutable = _resolvedExecutable();
   static String packageRoot = _packageRoot();
+  static var _resolution = () {
+    throw new UnimplementedError("TODO(iposva)");
+  } ();
 
-  // Cache the OS environemnt. This can be an OSError instance if
+  static Uri get packageRootUri {
+    if (_resolution is Uri) return _resolution;
+    return null;
+  }
+
+  static Map<String, Uri> get packageMap {
+    if (_resolution is Map) return _resolution;
+    if (_resolution == null) return const <String, Uri>{};
+    return null;
+  }
+
+  // Cache the OS environment. This can be an OSError instance if
   // retrieving the environment failed.
   static var _environmentCache;