An assert was being hit because WaitableEvent's dtor was calling CloseHandle ...

base/waitable_event.h

 // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_WAITABLE_EVENT_H_
 #define BASE_WAITABLE_EVENT_H_
 
 #include "base/basictypes.h"
 
 #if defined(OS_WIN)
@@ skipping 38 matching lines @@
   // consumer must call the Reset method.  If this parameter is false, then the
   // system automatically resets the event state to non-signaled after a single
   // waiting thread has been released.
   WaitableEvent(bool manual_reset, bool initially_signaled);
 
 #if defined(OS_WIN)
   // Create a WaitableEvent from an Event HANDLE which has already been
   // created. This objects takes ownership of the HANDLE and will close it when
   // deleted.
   explicit WaitableEvent(HANDLE event_handle);
+
+  // Releases ownership of the handle from this object.
+  HANDLE Release();
 #endif
 
   // WARNING: Destroying a WaitableEvent while threads are waiting on it is not
   // supported.  Doing so will cause crashes or other instability.
   ~WaitableEvent();
 
   // Put the event in the un-signaled state.
   void Reset();
 
   // Put the event in the signaled state.  Causing any thread blocked on Wait
@@ skipping 78 matching lines @@
   const bool manual_reset_;
   std::list<Waiter*> waiters_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(WaitableEvent);
 };
 
 }  // namespace base
 
 #endif  // BASE_WAITABLE_EVENT_H_