Create wrapper script around mojom's generate.dart in the Sky package.

mojo/dart/mojom/lib/generate.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /*
 * This script should be invoked via 'pub run' for an application that consumes
 * pub packages containing generated Mojo bindings (.mojom.dart files).
 *
 * It should be invoked as follows after 'pub get':
 * $ pub run mojom:generate
@@ skipping 115 matching lines @@
   await for (var package in packages.list()) {
     if (package is Directory) {
       installPackageMojoms(package, mojomPackage);
     }
   }
 
   for (var mojom_dir in additional_mojom_dirs) {
     copyMojomDirContents(mojom_dir, mojomPackage);
   }
 }