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

examples/js/share_echo.js

-#!mojo:js_content_handler
+#!mojo mojo:js_content_handler
 // Demonstrate using the ServiceProvider returned by the Shell
 // connectToApplication() method to provide a service to the
 // target application and to request a service from the target
 // application. To run this application with mojo_shell, set DIR
 // to be the absolute path for this directory, then:
 //   mojo_shell "file://$DIR/share_echo.js file://$DIR/share_echo_target.js"
 
 define("main", [
   "console",
   "mojo/services/public/js/application",
@@ skipping 24 matching lines @@
       targetSP.provideService(EchoService, EchoServiceImpl);
       var echoService = targetSP.requestService(EchoService);
       echoService.echoString("ShareEcho").then(function(response) {
         console.log(response.value);
       });
     }
   }
 
   return ShareEcho;
 });