Don't request missing favicon on every page request.

chrome/browser/favicon/favicon_service.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_SERVICE_H_
 #define CHROME_BROWSER_FAVICON_FAVICON_SERVICE_H_
 
 #include <vector>
 
 #include "base/callback.h"
+#include "base/hash_tables.h"
 #include "base/memory/ref_counted.h"
 #include "chrome/browser/common/cancelable_request.h"
 #include "chrome/browser/history/history_types.h"
 #include "chrome/browser/profiles/profile_keyed_service.h"
 #include "chrome/common/cancelable_task_tracker.h"
 #include "chrome/common/ref_counted_util.h"
 #include "ui/base/layout.h"
 
 class GURL;
 class HistoryService;
@@ skipping 195 matching lines @@
   // MergeFavicon() if it does not.
   // TODO(pkotwicz): Save unresized favicon bitmaps to the database.
   // TODO(pkotwicz): Support adding favicons for multiple icon URLs to the
   // thumbnail database.
   void SetFavicons(
       const GURL& page_url,
       const GURL& icon_url,
       history::IconType icon_type,
       const gfx::Image& image);
 
+  // Avoid repeated requests to download missing favicon (crbug.com/39402).

[sky, 2013/05/03 20:24:54]

Nuke crbug reference.

[mef, 2013/05/03 21:45:59]

Done.

+  void AddMissingFavicon(const GURL& icon_url);

[sky, 2013/05/03 20:24:54]

The names here are mildly confusing. How about:
UnableToDownloadFavicon();
WasUnableToDownloadingFavicon();
ClearUnableToDownloadURLs();

[mef, 2013/05/03 21:45:59]

Done.

+  bool IsMissingFavicon(const GURL& icon_url) const;
+  void ClearMissingFavicons();
+
  private:
+  typedef uint32 MissingFaviconURLHash;
+  base::hash_set<MissingFaviconURLHash> missing_favicon_urls_;
   HistoryService* history_service_;
 
   // Helper function for GetFaviconImageForURL(), GetRawFaviconForURL() and
   // GetFaviconForURL().
   CancelableTaskTracker::TaskId GetFaviconForURLImpl(
       const FaviconForURLParams& params,
       const std::vector<ui::ScaleFactor>& desired_scale_factors,
       const FaviconResultsCallback& callback,
       CancelableTaskTracker* tracker);
 
@@ skipping 12 matching lines @@
   void RunFaviconRawCallbackWithBitmapResults(
       const FaviconRawCallback& callback,
       int desired_size_in_dip,
       ui::ScaleFactor desired_scale_factor,
       const std::vector<history::FaviconBitmapResult>& favicon_bitmap_results);
 
   DISALLOW_COPY_AND_ASSIGN(FaviconService);
 };
 
 #endif  // CHROME_BROWSER_FAVICON_FAVICON_SERVICE_H_