Virtual destructors should have virtual keyword.

chrome/browser/extensions/image_loading_tracker.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 CHROME_BROWSER_EXTENSIONS_IMAGE_LOADING_TRACKER_H_
 #define CHROME_BROWSER_EXTENSIONS_IMAGE_LOADING_TRACKER_H_
 #pragma once
 
 #include <map>
 
@@ skipping 41 matching lines @@
     // image was not found or it failed to decode. |resource| is the
     // ExtensionResource where the |image| came from and the |index| represents
     // the index of the image just loaded (starts at 0 and increments every
     // time LoadImage is called).
     virtual void OnImageLoaded(SkBitmap* image,
                                const ExtensionResource& resource,
                                int index) = 0;
   };
 
   explicit ImageLoadingTracker(Observer* observer);
-  ~ImageLoadingTracker();
+  virtual ~ImageLoadingTracker();
 
   // Specify image resource to load. If the loaded image is larger than
   // |max_size| it will be resized to those dimensions. IMPORTANT NOTE: this
   // function may call back your observer synchronously (ie before it returns)
   // if the image was found in the cache.
   void LoadImage(const Extension* extension,
                  const ExtensionResource& resource,
                  const gfx::Size& max_size,
                  CacheParam cache);
 
@@ skipping 30 matching lines @@
   // integer identifies the id assigned to the request. If the extension is
   // deleted while fetching the image the entry is removed from the map.
   LoadMap load_map_;
 
   NotificationRegistrar registrar_;
 
   DISALLOW_COPY_AND_ASSIGN(ImageLoadingTracker);
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_IMAGE_LOADING_TRACKER_H_