Use ExitProcess on Windows.

runtime/bin/platform_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 "platform/globals.h"
 #if defined(TARGET_OS_WINDOWS)
 
 #include "bin/file.h"
 #include "bin/platform.h"
 #include "bin/log.h"
@@ skipping 87 matching lines @@
     return NULL;
   }
   char* path = StringUtilsWin::WideToUtf8(tmp_buffer);
   free(tmp_buffer);
   // Return the canonical path as the returned path might contain symlinks.
   char* canon_path = File::GetCanonicalPath(path);
   free(path);
   return canon_path;
 }
 
+void Platform::Exit(int exit_code) {
+  // On Windows we use ExitProcess so that threads can't clobber the exit_code.
+  // See: https://code.google.com/p/nativeclient/issues/detail?id=2870
+  ::ExitProcess(exit_code);
+}
+
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_WINDOWS)