Don't request missing favicon on every page request.

chrome/browser/favicon/favicon_service.cc

 // 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.
 
 #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"
 #include "chrome/browser/history/history_service.h"
 #include "chrome/browser/history/history_service_factory.h"
 #include "chrome/browser/history/select_favicon_frames.h"
 #include "chrome/browser/ui/webui/chrome_web_ui_controller_factory.h"
 #include "chrome/common/url_constants.h"
 #include "extensions/common/constants.h"
 #include "third_party/skia/include/core/SkBitmap.h"
@@ skipping 329 matching lines @@
   if (!gfx::PNGCodec::EncodeBGRASkBitmap(resized_image.AsBitmap(), false,
                                          &resized_bitmap_data)) {
     callback.Run(history::FaviconBitmapResult());
     return;
   }
 
   bitmap_result.bitmap_data = base::RefCountedBytes::TakeVector(
       &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.

+