Merge initial implementation of deferred handling in the VM:

runtime/lib/lib_prefix.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. 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";
 
 // This type corresponds to the VM-internal class LibraryPrefix.
 
 class _LibraryPrefix {
   _load() native "LibraryPrefix_load";
 
   loadLibrary() {
     var completer = new Completer<bool>();
     var port = new RawReceivePort();
     port.handler = (_) {
       this._load();
       completer.complete(true);
       port.close();
     };
     port.sendPort.send(1);
     return completer.future;
   }
 }