Allow tests to specify a package root.

dart/pkg/pkg.gyp

+# 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.
+
+{
+  'targets': [
+    {
+      'target_name': 'pkg_packages',
+      'type': 'none',
+      'actions': [
+        {
+          'action_name': 'make_pkg_packages',
+          'inputs': [
+            'args/lib',
+            'fixnum/lib',
+            'htmlescape/lib',
+            'http/lib',
+            'intl/lib',
+            'logging/lib',
+            'meta/lib',
+            'unittest/lib',
+            'webdriver/lib',
+          ],
+          'outputs': [
+            '<(PRODUCT_DIR)/packages/args',
+            '<(PRODUCT_DIR)/packages/fixnum',
+            '<(PRODUCT_DIR)/packages/htmlescape',
+            '<(PRODUCT_DIR)/packages/http',
+            '<(PRODUCT_DIR)/packages/intl',
+            '<(PRODUCT_DIR)/packages/logging',
+            '<(PRODUCT_DIR)/packages/meta',
+            '<(PRODUCT_DIR)/packages/unittest',
+            '<(PRODUCT_DIR)/packages/webdriver',
+          ],
+          'action': [
+            'python', '../tools/make_links.py',
+            '<(PRODUCT_DIR)/packages',
+            '<@(_inputs)',
+          ],
+        },
+      ],
+    }
+  ],
+}