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

services/js/test/echo.js

-#!mojo:js_content_handler
+#!mojo mojo:js_content_handler
 
 define("main", [
   "mojo/services/public/js/application",
   "services/js/test/echo_service.mojom"
 ], function(application, echoServiceMojom) {
 
   const Application = application.Application;
   const EchoService = echoServiceMojom.EchoService;
 
   class Echo extends Application {
     acceptConnection(url, serviceProvider) {
       var app = this;
       function EchoServiceImpl(client) {
         this.echoString = function(s) {
           if (s == "quit")
             app.quit();
           return Promise.resolve({value: s});
         };
       }
       serviceProvider.provideService(EchoService, EchoServiceImpl);
     }
   }
 
   return Echo;
 });