Correct thread state update order (fixes Windows crashes).

runtime/vm/thread_interrupter_macos.cc

 // Copyright (c) 2013, 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_MACOS)
 
 #include "vm/flags.h"
 #include "vm/os.h"
 #include "vm/signal_handler.h"
@@ skipping 29 matching lines @@
     its.lr = SignalHandler::GetLinkRegister(mcontext);
     state->callback(its, state->data);
   }
 };
 
 
 void ThreadInterrupter::InterruptThread(InterruptableThreadState* state) {
   if (FLAG_trace_thread_interrupter) {
     OS::Print("ThreadInterrupter interrupting %p\n", state->id);
   }
-  pthread_kill(state->id, SIGPROF);
+  int result = pthread_kill(state->id, SIGPROF);
+  ASSERT(result == 0);
 }
 
 
 void ThreadInterrupter::InstallSignalHandler() {
   SignalHandler::Install(ThreadInterrupterMacOS::ThreadInterruptSignalHandler);
 }
 
 
 void ThreadInterrupter::RemoveSignalHandler() {
   SignalHandler::Remove();
 }
 
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_MACOS)