Enables clean VM shutdown.

runtime/vm/gc_sweeper.cc

 // Copyright (c) 2011, 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.
 
 #include "vm/gc_sweeper.h"
 
 #include "vm/freelist.h"
 #include "vm/globals.h"
 #include "vm/heap.h"
 #include "vm/lockers.h"
@@ skipping 146 matching lines @@
 
 void GCSweeper::SweepConcurrent(Isolate* isolate,
                                 HeapPage* first,
                                 HeapPage* last,
                                 FreeList* freelist) {
   SweeperTask* task =
       new SweeperTask(isolate,
                       isolate->heap()->old_space(),
                       first, last,
                       freelist);
-  ThreadPool* pool = Dart::thread_pool();
-  pool->Run(task);
+  ThreadPool::Run(task);
 }
 
 }  // namespace dart