Terminate event handler thread on isolate shutdown.

runtime/bin/eventhandler_win.h

Index: runtime/bin/eventhandler_win.h
diff --git a/runtime/bin/eventhandler_win.h b/runtime/bin/eventhandler_win.h
index e64027c2bc3ade4d5a6b1e25c97faa327526c5a6..dd0a4fff67fe38edaec29e02947f74677f7cb3b2 100644
--- a/runtime/bin/eventhandler_win.h
+++ b/runtime/bin/eventhandler_win.h
@@ -348,6 +348,9 @@ class EventHandlerImplementation {
 
   void SendData(intptr_t id, Dart_Port dart_port, intptr_t data);
   void StartEventHandler();
+  void Shutdown();
+
+  static void EventHandlerEntry(uword args);
 
   DWORD GetTimeout();
   void HandleInterrupt(InterruptMessage* msg);
@@ -367,6 +370,7 @@ class EventHandlerImplementation {
 
   int64_t timeout_;  // Time for next timeout.
   Dart_Port timeout_port_;
+  bool shutdown_;
   HANDLE completion_port_;
 };