Rationalize Dart mojo and sky package structure

mojo/public/dart/lib/src/timer_queue.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.
 
 part of internal;
 
 class Timeout implements Comparable<Timeout> {
   int deadline; // milliseconds since the Unix epoch.
   SendPort port;
 
@@ skipping 33 matching lines @@
       _nextTimer = null;
     }
   }
 
   void removeCurrent() => updateTimer(currentPort, -1);
 
   bool get hasTimer => _nextTimer != null;
   int get currentTimeout => _nextTimer.deadline;
   SendPort get currentPort => _nextTimer.port;
 }