Fixed the racy code around the message-only window in base::MessagePumpForUI on Windows.

base/message_pump.h

Index: base/message_pump.h
diff --git a/base/message_pump.h b/base/message_pump.h
index b2e0a425656c6962f7d960d3637e68eab48cab36..407f8f866c1501d8a259a25f39105d0e3d88bbea 100644
--- a/base/message_pump.h
+++ b/base/message_pump.h
@@ -119,6 +119,10 @@ class BASE_EXPORT MessagePump : public RefCountedThreadSafe<MessagePump> {
   // used on the thread that called Run.
   virtual void ScheduleDelayedWork(const TimeTicks& delayed_work_time) = 0;
 
+  // Called directly by MessageLoop::~MessageLoop to clean up resources that
+  // must be freed on the MessageLoop's thread.
+  virtual void WillDestroyCurrentMessageLoop() {}
+
  protected:
   virtual ~MessagePump();
   friend class RefCountedThreadSafe<MessagePump>;