SSLClientSessionCache: Log number of times Lookup is called per Session.

net/ssl/ssl_client_session_cache.h

 // Copyright 2015 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 NET_SSL_SSL_CLIENT_SESSION_CACHE_H_
 #define NET_SSL_SSL_CLIENT_SESSION_CACHE_H_
 
 #include <stddef.h>
 #include <time.h>
 
@@ skipping 28 matching lines @@
     // The number of calls to Lookup before a new check for expired sessions.
     size_t expiration_check_count = 256;
   };
 
   explicit SSLClientSessionCache(const Config& config);
   ~SSLClientSessionCache() override;
 
   size_t size() const;
 
   // Returns the session associated with |cache_key| and moves it to the front
-  // of the MRU list. Returns nullptr if there is none.
-  bssl::UniquePtr<SSL_SESSION> Lookup(const std::string& cache_key);
+  // of the MRU list. Returns nullptr if there is none. If |count| is non-null,
+  // |*count| will contain the number of times this session has been looked up
+  // (including this call).
+  bssl::UniquePtr<SSL_SESSION> Lookup(const std::string& cache_key, int* count);
+
+  // Resets the count returned by Lookup to 0 for the session associated with
+  // |cache_key|.
+  void ResetLookupCount(const std::string& cache_key);
 
   // Inserts |session| into the cache at |cache_key|. If there is an existing
   // one, it is released. Every |expiration_check_count| calls, the cache is
   // checked for stale entries.
   void Insert(const std::string& cache_key, SSL_SESSION* session);
 
   // Removes all entries from the cache.
   void Flush();
 
   void SetClockForTesting(std::unique_ptr<base::Clock> clock);
 
   // Dumps memory allocation stats. |pmd| is the ProcessMemoryDump of the
   // browser process.
   void DumpMemoryStats(base::trace_event::ProcessMemoryDump* pmd);
 
  private:
+  struct Entry {
+    Entry();
+    Entry(Entry&&);
+    ~Entry();
+
+    int lookups;
+    bssl::UniquePtr<SSL_SESSION> session;
+  };
+
   // base::MemoryCoordinatorClient implementation:
   void OnMemoryStateChange(base::MemoryState state) override;
 
   // Returns true if |entry| is expired as of |now|.
   bool IsExpired(SSL_SESSION* session, time_t now);
 
   // Removes all expired sessions from the cache.
   void FlushExpiredSessions();
 
   // Clear cache on low memory notifications callback.
   void OnMemoryPressure(
       base::MemoryPressureListener::MemoryPressureLevel memory_pressure_level);
 
   std::unique_ptr<base::Clock> clock_;
   Config config_;
-  base::HashingMRUCache<std::string, bssl::UniquePtr<SSL_SESSION>> cache_;
+  base::HashingMRUCache<std::string, Entry> cache_;
   size_t lookups_since_flush_;
 
   // TODO(davidben): After https://crbug.com/458365 is fixed, replace this with
   // a ThreadChecker. The session cache should be single-threaded like other
   // classes in net.
   base::Lock lock_;
 
   std::unique_ptr<base::MemoryPressureListener> memory_pressure_listener_;
 
   DISALLOW_COPY_AND_ASSIGN(SSLClientSessionCache);
 };
 
 }  // namespace net
 
 #endif  // NET_SSL_SSL_CLIENT_SESSION_CACHE_H_