Don't request missing favicon on every page request.

chrome/browser/favicon/favicon_service.cc

Index: chrome/browser/favicon/favicon_service.cc
diff --git a/chrome/browser/favicon/favicon_service.cc b/chrome/browser/favicon/favicon_service.cc
index b762b19886e76adfb51da6044e1dc1c3cf85b05a..0cfa26d4d99cd9ca9d9d5d0a7c6f58725aed7139 100644
--- a/chrome/browser/favicon/favicon_service.cc
+++ b/chrome/browser/favicon/favicon_service.cc
@@ -4,6 +4,7 @@
 
 #include "chrome/browser/favicon/favicon_service.h"
 
+#include "base/hash.h"
 #include "base/message_loop_proxy.h"
 #include "chrome/browser/favicon/favicon_util.h"
 #include "chrome/browser/history/history_backend.h"
@@ -353,3 +354,13 @@ void FaviconService::RunFaviconRawCallbackWithBitmapResults(
       &resized_bitmap_data);
   callback.Run(bitmap_result);
 }
+
+void FaviconService::AddMissingFavicon(const GURL& icon_url) {
+  missing_favicon_urls_.insert(base::Hash(icon_url.spec()));

[mef, 2013/04/29 21:55:03]

Should I somehow protect this set from multi-threaded access?

[pauljensen, 2013/04/30 14:38:04]

I would always tend to say yes, but I don't see any thread checks in this file. 
If all calls are on the same thread and it looks like this will always be the
case, then maybe not.  I'm not knowledgeable enough when it comes to
FaviconService to give a good answer, an OWNER of this file would know best.

[mef, 2013/04/30 21:57:03]

Sounds good, will do.
On 2013/04/30 14:38:04, pauljensen wrote:

+}
+
+bool FaviconService::IsMissingFavicon(const GURL& icon_url) const {
+  int32 url_hash = base::Hash(icon_url.spec());
+  return missing_favicon_urls_.find(url_hash) != missing_favicon_urls_.end();
+}
+