Restructure public side of network service.

sky/framework/xmlhttprequest.sky

 <import src="/mojo/public/sky/core.sky" as="core" />
 <import src="/mojo/public/sky/unicode.sky" as="unicode" />
-<import src="/mojo/services/public/interfaces/network/network_service.mojom.sky" as="net" />
-<import src="/mojo/services/public/interfaces/network/url_loader.mojom.sky" as="loader" />
+<import src="/mojo/services/network/public/interfaces/network_service.mojom.sky" as="net" />
+<import src="/mojo/services/network/public/interfaces/url_loader.mojom.sky" as="loader" />
 <import src="shell.sky" as="shell" />
 <script>
 // XHR keeps itself alive.
 var outstandingRequests = new Set();
 
 const kPrivate = Symbol("XMLHttpRequestPrivate");
 
 class Private {
   constructor() {
     this.networkService = shell.connectToService(
@@ skipping 58 matching lines @@
       });
     }).catch(function(error) {
       outstandingRequests.delete(self);
       self.onerror(error);
     });
   }
 }
 
 module.exports = XMLHttpRequest;
 </script>