When a font family pref changes to the empty string, pass it to WebKit.

chrome/browser/ui/prefs/prefs_tab_helper.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_UI_PREFS_PREFS_TAB_HELPER_H_
 #define CHROME_BROWSER_UI_PREFS_PREFS_TAB_HELPER_H_
 
 #include "base/compiler_specific.h"
 #include "base/prefs/public/pref_change_registrar.h"
 #include "content/public/browser/notification_observer.h"
@@ skipping 27 matching lines @@
 
   // content::NotificationObserver overrides:
   virtual void Observe(int type,
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
 
   // Update the WebContents's RendererPreferences.
   void UpdateRendererPreferences();
 
   Profile* GetProfile();
+  void OnWebPrefChanged(const std::string& pref_name);
 
   content::WebContents* web_contents_;
   content::NotificationRegistrar registrar_;
   PrefChangeRegistrar pref_change_registrar_;
 
   DISALLOW_COPY_AND_ASSIGN(PrefsTabHelper);
 };
 
 #endif  // CHROME_BROWSER_UI_PREFS_PREFS_TAB_HELPER_H_