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

tests/standalone/io/platform_test.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.
 
 import "dart:async";
 import "dart:io";
 import "dart:isolate";
 
 import "package:async_helper/async_helper.dart";
 import "package:expect/expect.dart";
@@ skipping 30 matching lines @@
     Expect.equals(Platform.resolvedExecutable.substring(1, 3), ':\\');
   }
   // Move directory to be sure script is correct.
   var oldDir = Directory.current;
   Directory.current = Directory.current.parent;
   Expect.isTrue(Platform.script.path.
                 endsWith('tests/standalone/io/platform_test.dart'));
   Expect.isTrue(Platform.script.toFilePath().startsWith(oldDir.path));
   // Restore dir.
   Directory.current = oldDir;
-  Directory packageRoot = new Directory(Platform.packageRoot);
-  Expect.isTrue(packageRoot.existsSync());
-  Expect.isTrue(new Directory("${packageRoot.path}/expect").existsSync());
-  Expect.isTrue(Platform.executableArguments.any(
-      (arg) => arg.contains(Platform.packageRoot)));
+  Uri packageRoot = Platform.packageRoot;
+  Map packageMap = Platform.packageMap;
+  // One of packageRoot or packageMap is non-null.
+  Expect.isTrue((packageRoot == null) != (packageMap == null));
+  if (packageRoot != null) {
+    Directory packageDir = new Directory.fromUri(packageRoot);
+    Expect.isTrue(packageRoot.existsSync());
+    Expect.isTrue(new Directory("${packageRoot.path}/expect").existsSync());
+  } else {
+    Uri expectUri = packageMap["expect"];
+    Expect.isNotNull(expectUri);
+    Directory expectDir = new Directory.fromUri(expectUri);
+    Expect.isTrue(expectDir.existsSync());
+  }
 }
 
 void f(reply) {
   reply.send({"Platform.executable": Platform.executable,
               "Platform.script": Platform.script,
               "Platform.packageRoot": Platform.packageRoot,
               "Platform.executableArguments": Platform.executableArguments});
 }
 
 testIsolate() {
@@ skipping 66 matching lines @@
   Expect.throws(() => checkValidVersion('x.y.z'));
 }
 
 main() {
   // This tests assumes paths relative to dart main directory
   Directory.current = Platform.script.resolve('../../..').toFilePath();
   test();
   testIsolate();
   testVersion();
 }