Virtual destructors should have virtual keyword.

base/synchronization/waitable_event_watcher.h

 // Copyright (c) 2011 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_SYNCHRONIZATION_WAITABLE_EVENT_WATCHER_H_
 #define BASE_SYNCHRONIZATION_WAITABLE_EVENT_WATCHER_H_
 #pragma once
 
 #include "build/build_config.h"
 
@@ skipping 50 matching lines @@
 // -----------------------------------------------------------------------------
 
 class BASE_API WaitableEventWatcher
 #if defined(OS_POSIX)
     : public MessageLoop::DestructionObserver
 #endif
 {
  public:
 
   WaitableEventWatcher();
-  ~WaitableEventWatcher();
+  virtual ~WaitableEventWatcher();
 
   class Delegate {
    public:
     virtual ~Delegate() { }
 
     // -------------------------------------------------------------------------
     // This is called on the MessageLoop thread when WaitableEvent has been
     // signaled.
     //
     // Note: the event may not be signaled by the time that this function is
@@ skipping 73 matching lines @@
 #endif
 
   WaitableEvent* event_;
 
   Delegate* delegate_;
 };
 
 }  // namespace base
 
 #endif  // BASE_SYNCHRONIZATION_WAITABLE_EVENT_WATCHER_H_