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..fb5a8bce981fdef139fc571999f668a98fe08253 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 +354,19 @@ void FaviconService::RunFaviconRawCallbackWithBitmapResults(
       &resized_bitmap_data);
   callback.Run(bitmap_result);
 }
+
+void FaviconService::AddMissingFavicon(const GURL& icon_url) {

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

Order should match header.

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

Done.

+  MissingFaviconURLHash url_hash = base::Hash(icon_url.spec());

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

How likely are we to get false collisions?

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

With ideal Hash it should be 1/2**32 ~ 25*(10**-11). Not very likely, but
theoretically possible. I was going for minimization of memory and performance
impact.

On 2013/05/03 20:24:54, sky wrote:

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

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

nit: nuke newlines.

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

Done.

+