Modify scanner and parser to be standalone packages.

pkg/dart_parser/bin/parser.dart

Index: pkg/dart_parser/bin/parser.dart
diff --git a/pkg/dart_parser/bin/parser.dart b/pkg/dart_parser/bin/parser.dart
new file mode 100644
index 0000000000000000000000000000000000000000..c9c50568bc8718d4999fd7cf9fd038ecac0f73e5
--- /dev/null
+++ b/pkg/dart_parser/bin/parser.dart
@@ -0,0 +1,7 @@
+// 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.
+
+import 'package:parser/src/main.dart' as parser;
+
+main(List<String> arguments) => parser.main(arguments);