Rationalize Dart mojo and sky package structure

services/dart/test/pingpong_target/main.dart

 // Copyright 2015 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.
 
 import 'dart:async';
 
-import 'package:mojo/public/dart/application.dart';
-import 'package:mojo/public/dart/bindings.dart';
-import 'package:mojo/public/dart/core.dart';
+import 'package:mojo/application.dart';
+import 'package:mojo/bindings.dart';
+import 'package:mojo/core.dart';
 
 import 'package:mojom/dart/test/pingpong_service.mojom.dart';
 
 class PingPongServiceImpl implements PingPongService {
   PingPongServiceStub _stub;
   Application _application;
   PingPongClientProxy _pingPongClient;
 
   PingPongServiceImpl(this._application, MojoMessagePipeEndpoint endpoint) {
     _stub = new PingPongServiceStub.fromEndpoint(endpoint, this);
@@ skipping 40 matching lines @@
     await close();
     assert(MojoHandle.reportLeakedHandles());
   }
 }
 
 main(List args) {
   MojoHandle appHandle = new MojoHandle(args[0]);
   String url = args[1];
   new PingPongApplication.fromHandle(appHandle);
 }