Move the JS content handler et al from mojo/apps/js to mojo/services

examples/js/main.js

 // 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.
 
 // This trivial app just loads "cnn.com" using the Mojo Network and URLLoader
 // services and then prints a brief summary of the response.
 //
 // To run it this file must be specified as a URL. For
 // example:
 //   (cd YOUR_DIR/mojo/apps/js; python -m SimpleHTTPServer ) &
@@ skipping 32 matching lines @@
     for(var key in result.response)
       console.log(key + " => " + result.response[key]);
     var drainDataPromise = core.drainData(result.response.body);
     drainDataPromise.then(function(result) {
       console.log("read " + result.buffer.byteLength + " bytes");
     }).then(function() {
       mojo.quit();
     });
   });
 });