[Extension UI] Observing WebContentsObserver from extension_settings_handler.cc

chrome/browser/ui/webui/extensions/extension_settings_handler.cc

 // 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.
 
 #include "chrome/browser/ui/webui/extensions/extension_settings_handler.h"
 
 #include <vector>
 
 #include "base/prefs/pref_service.h"
 #include "base/strings/string_util.h"
@@ skipping 267 matching lines @@
 }
 
 void ExtensionSettingsHandler::RegisterMessages() {
   Profile* profile = Profile::FromWebUI(web_ui())->GetOriginalProfile();
   extension_service_ =
       extensions::ExtensionSystem::Get(profile)->extension_service();
   // Clear the preference for the ADT Promo before fully removing it.
   // TODO(devlin): Take this out when everyone's been updated.
   Profile::FromWebUI(web_ui())->GetPrefs()->ClearPref(
       prefs::kExtensionsUIDismissedADTPromo);
+
+  content::WebContentsObserver::Observe(web_ui()->GetWebContents());
 }
 
 void ExtensionSettingsHandler::ReloadUnpackedExtensions() {
   ExtensionRegistry* registry =
       ExtensionRegistry::Get(extension_service_->profile());
   std::vector<const Extension*> unpacked_extensions;
   for (const scoped_refptr<const extensions::Extension>& extension :
        registry->enabled_extensions()) {
     if (Manifest::IsUnpackedLocation(extension->location()))
       unpacked_extensions.push_back(extension.get());
   }
 
   for (std::vector<const Extension*>::iterator iter =
        unpacked_extensions.begin(); iter != unpacked_extensions.end(); ++iter) {
     extension_service_->ReloadExtensionWithQuietFailure((*iter)->id());
   }
 }
 
 }  // namespace extensions