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

net/http/http_cache_transaction.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.
 
 // This file declares HttpCache::Transaction, a private class of HttpCache so
 // it should only be included by http_cache.cc
 
 #ifndef NET_HTTP_HTTP_CACHE_TRANSACTION_H_
 #define NET_HTTP_HTTP_CACHE_TRANSACTION_H_
 
@@ skipping 327 matching lines @@
   // Returns network error code.
   int RestartNetworkRequestWithAuth(const AuthCredentials& credentials);
 
   // Called to determine if we need to validate the cache entry before using it.
   bool RequiresValidation();
 
   // Called to make the request conditional (to ask the server if the cached
   // copy is valid).  Returns true if able to make the request conditional.
   bool ConditionalizeRequest();
 
+  // Determins if saved response permits conditionalization, and extracts
+  // etag/last-modified values. Only depends on response_.headers.
+  bool ResponseConditionalizable(std::string* etag_value,
+                                 std::string* last_modified_value);
+
   // Makes sure that a 206 response is expected.  Returns true on success.
   // On success, handling_206_ will be set to true if we are processing a
   // partial entry.
   bool ValidatePartialResponse();
 
   // Handles a response validation error by bypassing the cache.
   void IgnoreRangeRequest();
 
   // Fixes the response headers to match expectations for a HEAD request.
   void FixHeadersForHead();
@@ skipping 157 matching lines @@
   bool in_do_loop_;
 
   base::WeakPtrFactory<Transaction> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(Transaction);
 };
 
 }  // namespace net
 
 #endif  // NET_HTTP_HTTP_CACHE_TRANSACTION_H_