Don't request missing favicon on every page request.

chrome/browser/favicon/favicon_service.h

Index: chrome/browser/favicon/favicon_service.h
diff --git a/chrome/browser/favicon/favicon_service.h b/chrome/browser/favicon/favicon_service.h
index 12ad68834af2e8c2b0c41d159564fd19ade4bf12..bbebdf16ee78cf57b1de8f985f753f9638bc5c32 100644
--- a/chrome/browser/favicon/favicon_service.h
+++ b/chrome/browser/favicon/favicon_service.h
@@ -8,6 +8,7 @@
 #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"
@@ -223,7 +224,14 @@ class FaviconService : public CancelableRequestProvider,
       history::IconType icon_type,
       const gfx::Image& image);
 
+  // Avoid repeated requests to download missing favicon.
+  void UnableToDownloadFavicon(const GURL& icon_url);
+  bool WasUnableToDownloadFavicon(const GURL& icon_url) const;
+  void ClearUnableToDownloadFavicons();
+
  private:
+  typedef uint32 MissingFaviconURLHash;
+  base::hash_set<MissingFaviconURLHash> missing_favicon_urls_;
   HistoryService* history_service_;
 
   // Helper function for GetFaviconImageForURL(), GetRawFaviconForURL() and