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

net/disk_cache/disk_cache.h

Index: net/disk_cache/disk_cache.h
diff --git a/net/disk_cache/disk_cache.h b/net/disk_cache/disk_cache.h
index 4a3ae119b53f9c90b22f5c70379e5d4fb0f1f057..19fcf0529c56d27a1d0f4fc921e3c07ab947b58f 100644
--- a/net/disk_cache/disk_cache.h
+++ b/net/disk_cache/disk_cache.h
@@ -184,6 +184,15 @@ class NET_EXPORT Backend {
   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.