Modify scanner and parser to be standalone packages.

pkg/dart_scanner/bin/scanner.dart

Index: pkg/dart_scanner/bin/scanner.dart
diff --git a/pkg/dart_scanner/bin/scanner.dart b/pkg/dart_scanner/bin/scanner.dart
new file mode 100644
index 0000000000000000000000000000000000000000..169bc1a74707af3dc3a39f2e3794d9dd7fd1e64b
--- /dev/null
+++ b/pkg/dart_scanner/bin/scanner.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.md file.
+
+import 'package:scanner/src/main.dart' as scanner;
+
+main(List<String> arguments) => scanner.main(arguments);