Dart: Removes name conflicts from generated bindings.

sky/tests/services/network.sky

 #!mojo mojo:sky_viewer
 <sky>
 <script>
 import '/sky/framework/embedder.dart';
 import 'dart:async';
 import 'dart:typed_data';
 import "dart:sky.internals" as internals;
 import 'mojo:bindings';
 import 'mojo:core';
 
 import 'package:mojo/services/network/public/interfaces/network_service.mojom.dart';
 import 'package:mojo/services/network/public/interfaces/url_loader.mojom.dart';
 
 Future<String> run(url) async {
-  var networkService = new NetworkServiceProxy.unbound();
-  embedder.connectToService("mojo:network_service", networkService);
+  var networkServiceProxy = new NetworkServiceProxy.unbound();
+  var networkService = networkServiceProxy.interface;
+  embedder.connectToService("mojo:network_service", networkServiceProxy);
 
   var urlLoaderProxy = new UrlLoaderProxy.unbound();
+  var urlLoader = urlLoaderProxy.interface;
   networkService.createUrlLoader(urlLoaderProxy);
 
   var urlRequest = new UrlRequest()
       ..url = url
       ..autoFollowRedirects = true;
-  var urlResponse = await urlLoaderProxy.start(urlRequest);
+  var urlResponse = await urlLoader.start(urlRequest);
 
-  urlLoaderProxy.close();
-  networkService.close();
+  urlLoaderProxy.impl.close();
+  networkServiceProxy.impl.close();
 
   print("url => ${urlResponse.response.url}");
   print("status_line => ${urlResponse.response.statusLine}");
   print("mime_type => ${urlResponse.response.mimeType}");
 
   ByteData bodyData =
       await DataPipeDrainer.drainHandle(urlResponse.response.body);
   print("read ${bodyData.lengthInBytes} bytes");
 
   return new String.fromCharCodes(new Uint8List.view(bodyData.buffer));
 }
 
 main() async {
   var url = "http://127.0.0.1:8000/sky/tests/services/resources/pass.txt";
   var result = await run(url);
   internals.notifyTestComplete(result);
 }
 </script>
 </sky>