Don't request missing favicon on every page request.

chrome/browser/favicon/favicon_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_FAVICON_FAVICON_TAB_HELPER_H_
 #define CHROME_BROWSER_FAVICON_FAVICON_TAB_HELPER_H_
 
 #include <vector>
 
 #include "base/basictypes.h"
@@ skipping 69 matching lines @@
   virtual void NavigateToPendingEntry(
       const GURL& url,
       content::NavigationController::ReloadType reload_type) OVERRIDE;
   virtual void DidNavigateMainFrame(
       const content::LoadCommittedDetails& details,
       const content::FrameNavigateParams& params) OVERRIDE;
 
   // Favicon download callback.
   void DidDownloadFavicon(
       int id,
+      int http_status_code,
       const GURL& image_url,
       int requested_size,
       const std::vector<SkBitmap>& bitmaps);
 
   Profile* profile_;
   bool should_fetch_icons_;
 
   scoped_ptr<FaviconHandler> favicon_handler_;
 
   // Handles downloading touchicons. It is NULL if
   // browser_defaults::kEnableTouchIcon is false.
   scoped_ptr<FaviconHandler> touch_icon_handler_;
 
   DISALLOW_COPY_AND_ASSIGN(FaviconTabHelper);
 };
 
 #endif  // CHROME_BROWSER_FAVICON_FAVICON_TAB_HELPER_H_