RFC: use some in-memory state in SimpleCache to quickly cache-miss some CantConditionalize cases

net/disk_cache/disk_cache.h

 // 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.
 
 // Defines the public interface of the disk cache. For more details see
 // http://dev.chromium.org/developers/design-documents/network-stack/disk-cache
 
 #ifndef NET_DISK_CACHE_DISK_CACHE_H_
 #define NET_DISK_CACHE_DISK_CACHE_H_
 
@@ skipping 166 matching lines @@
   virtual void GetStats(base::StringPairs* stats) = 0;
 
   // Called whenever an external cache in the system reuses the resource
   // referred to by |key|.
   virtual void OnExternalCacheHit(const std::string& key) = 0;
 
   // Returns the estimate of dynamically allocated memory in bytes.
   virtual size_t DumpMemoryStats(
       base::trace_event::ProcessMemoryDump* pmd,
       const std::string& parent_absolute_name) const = 0;
+
+  // Backends can optionally permit one to store, probabilistically, up to a
+  // byte associated with a key (for an existing entry). Accessing the key is
+  // guaranteed to be cheap, but the method is permitted to return 0, and may,
+  // with low probability, even return values associated with the wrong key in
+  // case of collisions. Therefore it should not be used to make decisions that
+  // affect correctness (especially security).
+  virtual uint8_t GetMemoryEntryData(const std::string& key);
+  virtual void SetMemoryEntryData(const std::string& key, uint8_t data);
 };
 
 // This interface represents an entry in the disk cache.
 class NET_EXPORT Entry {
  public:
   typedef net::CompletionCallback CompletionCallback;
   typedef net::IOBuffer IOBuffer;
 
   // Marks this cache entry for deletion.
   virtual void Doom() = 0;
@@ skipping 156 matching lines @@
     entry->Close();
   }
 };
 
 // Automatically closes an entry when it goes out of scope.
 typedef std::unique_ptr<Entry, EntryDeleter> ScopedEntryPtr;
 
 }  // namespace disk_cache
 
 #endif  // NET_DISK_CACHE_DISK_CACHE_H_