Rationalize Dart mojo and sky package structure

mojo/public/dart/lib/src/handle.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 core;
 
 class _HandleCreationRecord {
   final MojoHandle handle;
   final StackTrace stack;
   _HandleCreationRecord(this.handle, this.stack);
@@ skipping 112 matching lines @@
       var handleCreation = MojoHandle._unclosedHandles[handle];
       if (handleCreation != null) {
         print("HANDLE LEAK: handle: $handle, created at:");
         print("${handleCreation.stack}");
         noleaks = false;
       }
     }
     return noleaks;
   }
 }