Rationalize Dart mojo and sky package structure

sky/sdk/lib/framework/editing/keyboard.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 '../shell.dart' as shell;
 import 'package:mojom/keyboard/keyboard.mojom.dart';
 
 class _KeyboardConnection {
   KeyboardServiceProxy proxy;
 
   _KeyboardConnection() {
     proxy = new KeyboardServiceProxy.unbound();
     shell.requestService("mojo:keyboard", proxy);
   }
 
   KeyboardService get keyboard => proxy.ptr;
 }
 
 final _KeyboardConnection _connection = new _KeyboardConnection();
 final KeyboardService keyboard = _connection.keyboard;