Add a class to replace ImageLoadingTracker with a nicer API.

chrome/browser/extensions/navigation_observer.h

 // Copyright (c) 2012 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_NAVIGATION_OBSERVER_H_
 #define CHROME_BROWSER_EXTENSIONS_NAVIGATION_OBSERVER_H_
 
 #include <set>
 #include <string>
 
 #include "base/memory/scoped_ptr.h"
 #include "chrome/browser/extensions/extension_install_prompt.h"
+#include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 
 class Profile;
 
 namespace content {
 class NavigationController;
 }
 
 namespace extensions {
 
@@ skipping 38 matching lines @@
 
   // The extension ids we've already prompted the user about.
   std::set<std::string> prompted_extensions_;
 
   DISALLOW_COPY_AND_ASSIGN(NavigationObserver);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_NAVIGATION_OBSERVER_H_