Changes magic sequence to '!#mojo ' and strips 'mojo ' when building url

examples/js/cube.js

-#!mojo:js_content_handler
+#!mojo mojo:js_content_handler
 
 // Copyright 2014 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.
 
 define("main", [
   "console",
   "mojo/services/public/js/application",
   "mojo/services/geometry/public/interfaces/geometry.mojom",
   "mojo/services/gpu/public/interfaces/gpu.mojom",
@@ skipping 397 matching lines @@
         this.gles2_.setDimensions(size);
     }
 
     onDestroyed() {
       this.quit();
     }
   }
 
   return CubeDemo;
 });