Automatic thread cleanup on non-Windows platforms.

runtime/vm/thread.cc

Index: runtime/vm/thread.cc
===================================================================
--- runtime/vm/thread.cc	(revision 45810)
+++ runtime/vm/thread.cc	(working copy)
@@ -18,9 +18,14 @@
 ThreadLocalKey Thread::thread_key_ = OSThread::kUnsetThreadLocalKey;
 
 
+static void DeleteThread(void* thread) {
+  delete reinterpret_cast<Thread*>(thread);
+}
+
+
 void Thread::InitOnce() {
   ASSERT(thread_key_ == OSThread::kUnsetThreadLocalKey);
-  thread_key_ = OSThread::CreateThreadLocal();
+  thread_key_ = OSThread::CreateThreadLocal(DeleteThread);
   ASSERT(thread_key_ != OSThread::kUnsetThreadLocalKey);
 }
 
@@ -37,6 +42,7 @@
 }
 
 
+#if defined(TARGET_OS_WINDOWS)
 void Thread::CleanUp() {
   Thread* current = Current();
   if (current != NULL) {
@@ -44,6 +50,7 @@
   }
   SetCurrent(NULL);
 }
+#endif
 
 
 void Thread::EnterIsolate(Isolate* isolate) {