Add the "virtual" keyword on method overrides that are missing it.

net/base/listen_socket.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.
 
 // TCP/IP server that handles IO asynchronously in the specified MessageLoop.
 // These objects are NOT thread safe.  They use WSAEVENT handles to monitor
 // activity in a given MessageLoop.  This means that callbacks will
 // happen in that loop's thread always and that all other methods (including
 // constructors and destructors) should also be called from the same thread.
 
@@ skipping 96 matching lines @@
 #if defined(OS_WIN)
   // ObjectWatcher delegate
   virtual void OnObjectSignaled(HANDLE object);
   base::ObjectWatcher watcher_;
   HANDLE socket_event_;
 #elif defined(OS_POSIX)
   WaitState wait_state_;
   // The socket's libevent wrapper
   MessageLoopForIO::FileDescriptorWatcher watcher_;
   // Called by MessagePumpLibevent when the socket is ready to do I/O
-  void OnFileCanReadWithoutBlocking(int fd);
-  void OnFileCanWriteWithoutBlocking(int fd);
+  virtual void OnFileCanReadWithoutBlocking(int fd);
+  virtual void OnFileCanWriteWithoutBlocking(int fd);
 #endif
 
   SOCKET socket_;
   ListenSocketDelegate *socket_delegate_;
 
  private:
   bool reads_paused_;
   bool has_pending_reads_;
 
   DISALLOW_COPY_AND_ASSIGN(ListenSocket);
 };
 
 #endif  // NET_BASE_LISTEN_SOCKET_H_