Add undeclared virtual destructors part 2...

chrome_frame/test/window_watchdog.h

 // Copyright (c) 2010 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_FRAME_TEST_WINDOW_WATCHDOG_H_
 #define CHROME_FRAME_TEST_WINDOW_WATCHDOG_H_
 
 #include <windows.h>
 
 #include <string>
 #include <vector>
 
 struct FunctionStub;
 
 // Interface implemented by WindowWatchdog users. An observer can register
 // for notifications on multiple window classes.
 class WindowObserver {  // NOLINT
  public:
   virtual void OnWindowDetected(HWND hwnd, const std::string& caption) = 0;
+
+ protected:
+  virtual ~WindowObserver() {}
 };
 
 // Watch a for window to be shown with the given window class name.
 // If found, call the observer interested in it.
 class WindowWatchdog {
  public:
   WindowWatchdog();
   ~WindowWatchdog();
 
   // Register for notifications for |window_class|. An observer can register
@@ skipping 21 matching lines @@
 
   typedef std::vector<WindowObserverEntry> ObserverMap;
 
   HWINEVENTHOOK hook_;
   ObserverMap observers_;
   FunctionStub* hook_stub_;
 };
 
 
 #endif  // CHROME_FRAME_TEST_WINDOW_WATCHDOG_H_