Terminate worker threads before detaching main thread.

Source/core/Init.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 105 matching lines @@
     ScriptStreamerThread::init();
 }
 
 void CoreInitializer::shutdown()
 {
     // Make sure we stop the HTMLParserThread and ScriptStreamerThread before
     // Platform::current() is cleared.
     ScriptStreamerThread::shutdown();
     HTMLParserThread::shutdown();
 
-    // Make sure we stop WorkerThreads before Partition::shutdown() which frees ExecutionContext.
-    WorkerThread::terminateAndWaitForAllWorkers();
-
     Partitions::shutdown();
 }
 
 } // namespace blink