Add package implementation.

lib/package_resolver.dart

Index: lib/package_resolver.dart
diff --git a/lib/package_resolver.dart b/lib/package_resolver.dart
new file mode 100644
index 0000000000000000000000000000000000000000..c0984d377c9c1e28e99fc0f44497d727bde17198
--- /dev/null
+++ b/lib/package_resolver.dart
@@ -0,0 +1,6 @@
+// Copyright (c) 2016, 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.
+
+export 'src/package_resolver.dart';
+export 'src/sync_package_resolver.dart';