Add undeclared virtual destructors part 2...

chrome/common/deprecated/event_sys.h

 // Copyright (c) 2009 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 CHROME_COMMON_DEPRECATED_EVENT_SYS_H_
 #define CHROME_COMMON_DEPRECATED_EVENT_SYS_H_
 
 // TODO: This class should be removed or moved to Notifier code.
 // See Bug 42450 (http://code.google.com/p/chromium/issues/detail?id=42450).
 
 class AutoLock;
 class Lock;
 
 // An abstract base class for listening to events.
 //
 // Don't inherit from this class yourself. Using NewEventListenerHookup() is
 // much easier.
 template <typename EventType>
 class EventListener {
  public:
   virtual void HandleEvent(const EventType& event) = 0;
+
+ protected:
+  virtual ~EventListener() {}
 };
 
 // See the -inl.h for details about the following.
 
 template <typename EventTraits, typename NotifyLock = Lock,
           typename ScopedNotifyLocker = AutoLock>
 class EventChannel;
 
 class EventListenerHookup;
 
 template <typename EventChannel, typename CallbackObject,
           typename CallbackMethod>
 EventListenerHookup* NewEventListenerHookup(EventChannel* channel,
                                             CallbackObject* cbobject,
                                             CallbackMethod cbmethod);
 
 template <typename EventChannel, typename CallbackObject,
           typename CallbackMethod, typename CallbackArg0>
 EventListenerHookup* NewEventListenerHookup(EventChannel* channel,
                                             CallbackObject* cbobject,
                                             CallbackMethod cbmethod,
                                             CallbackArg0 arg0);
 
 #endif  // CHROME_COMMON_DEPRECATED_EVENT_SYS_H_