Rationalize Dart mojo and sky package structure

services/dart/test/pingpong/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 PingPongClientImpl implements PingPongClient {
   final PingPongClientStub stub;
   Completer _completer;
   int _count;
 
   PingPongClientImpl.unbound(this._count, this._completer)
       : stub = new PingPongClientStub.unbound() {
@@ skipping 97 matching lines @@
 }
 
 main(List args) {
   MojoHandle appHandle = new MojoHandle(args[0]);
   String url = args[1];
   new PingPongApplication.fromHandle(appHandle)
     ..onError = (() {
       assert(MojoHandle.reportLeakedHandles());
     });
 }