Rationalize Dart mojo and sky package structure

mojo/dart/test/control_messages_test.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 'dart:isolate';
 import 'dart:typed_data';
 
-import 'package:mojo/dart/testing/expect.dart';
-import 'package:mojo/public/dart/bindings.dart' as bindings;
-import 'package:mojo/public/dart/core.dart' as core;
+import 'package:testing/expect.dart';
+import 'package:mojo/bindings.dart' as bindings;
+import 'package:mojo/core.dart' as core;
 import 'package:mojom/sample/sample_interfaces.mojom.dart' as sample;
 
 // Bump this if sample_interfaces.mojom adds higher versions.
 const maxVersion = 3;
 
 // Implementation of IntegerAccessor.
 class IntegerAccessorImpl implements sample.IntegerAccessor {
   // Some initial value.
   int _value = 0;
 
@@ skipping 77 matching lines @@
   }
   Expect.isTrue(exceptionCaught);
   closeProxyAndStub(ps);
 }
 
 main() async {
   await testQueryVersion();
   await testRequireVersionSuccess();
   await testRequireVersionDisconnect();
 }