Rationalize Dart mojo and sky package structure

mojo/dart/test/bindings_generation_test.dart

 // Copyright 2014 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;
 import 'package:mojom/mojo/test/test_structs.mojom.dart' as structs;
 import 'package:mojom/mojo/test/rect.mojom.dart' as rect;
 
 class ProviderImpl implements sample.Provider {
   sample.ProviderStub _stub;
 
   ProviderImpl(core.MojoMessagePipeEndpoint endpoint) {
     _stub = new sample.ProviderStub.fromEndpoint(endpoint, this);
   }
@@ skipping 104 matching lines @@
     Expect.isTrue(b);
   });
 }
 
 main() async {
   testSerializeStructs();
   await testCallResponse();
   await testAwaitCallResponse();
   await runOnClosedTest();
 }