Wait for exit-code thread to terminate before terminating main.

runtime/bin/process_win.cc

 // Copyright (c) 2012, 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 <process.h>
 
 #include "bin/builtin.h"
 #include "bin/process.h"
 #include "bin/eventhandler.h"
 #include "platform/globals.h"
@@ skipping 394 matching lines @@
       return false;
     }
   }
   return true;
 }
 
 
 void Process::Exit(intptr_t id) {
   RemoveProcess(id);
 }
+
+
+void Process::TerminateExitCodeHandler() {
+  // TODO(ager): Implement.
+}