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

chrome/browser/autocomplete/keyword_provider.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.
 //
 // This file contains the keyword autocomplete provider. The keyword provider
 // is responsible for remembering/suggesting user "search keyword queries"
 // (e.g.  "imdb Godzilla") and then fixing them up into valid URLs.  An
 // instance of it gets created and managed by the autocomplete controller.
 // KeywordProvider uses a TemplateURLModel to find the set of keywords.
 //
@@ skipping 108 matching lines @@
       const std::wstring& keyword,
       const AutocompleteInput& input,
       size_t prefix_length,
       const std::wstring& remaining_input,
       int relevance);
 
   void EnterExtensionKeywordMode(const std::string& extension_id);
   void MaybeEndExtensionKeywordMode();
 
   // NotificationObserver interface.
-  void Observe(NotificationType type,
-               const NotificationSource& source,
-               const NotificationDetails& details);
+  virtual void Observe(NotificationType type,
+                       const NotificationSource& source,
+                       const NotificationDetails& details);
 
   // Model for the keywords.  This is only non-null when testing, otherwise the
   // TemplateURLModel from the Profile is used.
   TemplateURLModel* model_;
 
   // Identifies the current input state. This is incremented each time the
   // autocomplete edit's input changes in any way. It is used to tell whether
   // suggest results from the extension are current.
   int current_input_id_;
 
   // The input state at the time we last asked the extension for suggest
   // results.
   AutocompleteInput extension_suggest_last_input_;
 
   // We remember the last suggestions we've received from the extension in case
   // we need to reset our matches without asking the extension again.
   std::vector<AutocompleteMatch> extension_suggest_matches_;
 
   // If non-empty, holds the ID of the extension whose keyword is currently in
   // the URL bar while the autocomplete popup is open.
   std::string current_keyword_extension_id_;
 
   NotificationRegistrar registrar_;
 
   DISALLOW_COPY_AND_ASSIGN(KeywordProvider);
 };
 
 #endif  // CHROME_BROWSER_AUTOCOMPLETE_KEYWORD_PROVIDER_H_