Use ExitProcess on Windows.

runtime/vm/thread.cc

Index: runtime/vm/thread.cc
diff --git a/runtime/vm/thread.cc b/runtime/vm/thread.cc
index 5c635b9be57e6009e06a129f78d01e162070cffa..5e5266629120ad4b38ed3567f30dc74548f4e8f8 100644
--- a/runtime/vm/thread.cc
+++ b/runtime/vm/thread.cc
@@ -125,6 +125,19 @@ static void DeleteThread(void* thread) {
 
 void Thread::Shutdown() {
   if (thread_list_lock_ != NULL) {
+    Thread* thread = Current();
+    ASSERT(thread != NULL);
+    delete thread;
+    thread = NULL;
+    SetCurrent(NULL);
+    OSThread::DeleteThreadLocal(thread_key_);

[Cutch, 2015/10/28 20:33:15]

Can we move this TLS cleanup below the ASSERT. 

Once we know we have no more threads we don't ever care about the TLS
destructor.

[zra, 2015/10/28 21:40:04]

Moved.
I was hitting a crash where ~Thread() was running called from DeleteThread()
after Shutdown(), so I'm a bit paranoid about cleaning up the TLS now.

+    thread_key_ = OSThread::kUnsetThreadLocalKey;
+
+    // Check that there are no more threads, then delete the lock.
+    {
+      MutexLocker ml(thread_list_lock_);
+      ASSERT(thread_list_head_ == NULL);
+    }
     delete thread_list_lock_;
     thread_list_lock_ = NULL;
   }