Fix deferred load code in checked mode

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 {
 
   bool _load() native "LibraryPrefix_load";
 
-  void _invalidateDependentCode()
+  bool _invalidateDependentCode()
       native "LibraryPrefix_invalidateDependentCode";
 
   loadLibrary() {
     var completer = _outstandingLoadRequests[this];
     if (completer != null) {
       return completer.future;
     }
     completer = new Completer<bool>();
     _outstandingLoadRequests[this] = completer;
     Timer.run(() {
@@ skipping 19 matching lines @@
 // Called from the VM when all outstanding load requests have
 // finished.
 _completeDeferredLoads() {
   var lenghth = _outstandingLoadRequests;
   _outstandingLoadRequests.forEach((prefix, completer) {
     prefix._invalidateDependentCode();
     completer.complete(true);
   });
   _outstandingLoadRequests.clear();
 }