Add the UMA recording recall of URLRequests preconnected.

chrome/browser/net/timed_cache.h

+// Copyright 2013 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_NET_TIMED_CACHE_H_
+#define CHROME_BROWSER_NET_TIMED_CACHE_H_
+
+#include "base/basictypes.h"
+#include "base/containers/mru_cache.h"
+#include "base/time.h"
+
+class GURL;
+
+namespace chrome_browser_net {
+
+// Define a LRU cache that recalls all navigations within the last N seconds.
+// When we learn about subresources to possibly preconnect to, it would be a
+// waste to preconnect when the original navigation was too long ago.  Any
+// connected, but unused TCP/IP connection, will generally be reset by the
+// server if it is not used quickly (i.e., GET or POST is sent).
+class TimedCache {
+ public:
+  explicit TimedCache(const base::TimeDelta& max_duration);
+  ~TimedCache();
+
+  // Evicts any entries that have been in the FIFO "too long," and then checks
+  // to see if the given url is (still) in the FIFO cache.
+  bool WasRecentlySeen(const GURL& url);
+
+  // Adds the given url to the cache, where it will remain for max_duration_.
+  void SetRecentlySeen(const GURL& url);
+
+ private:
+  // Our cache will be keyed on a URL (actually, just a scheme/host/port).
+  // We will always track the time it was last added to the FIFO cache by
+  // remembering a TimeTicks value.
+  typedef base::MRUCache<GURL, base::TimeTicks> UrlMruTimedCache;
+  UrlMruTimedCache mru_cache_;
+
+  // The longest time an entry can persist in the cache, and still be found.
+  const base::TimeDelta max_duration_;
+
+  DISALLOW_COPY_AND_ASSIGN(TimedCache);
+};
+
+}  // namespace chrome_browser_net
+
+#endif  // CHROME_BROWSER_NET_TIMED_CACHE_H_