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

net/disk_cache/simple/simple_index_file.h

 // Copyright (c) 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 NET_DISK_CACHE_SIMPLE_SIMPLE_INDEX_FILE_H_
 #define NET_DISK_CACHE_SIMPLE_SIMPLE_INDEX_FILE_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 49 matching lines @@
                   uint64_t entry_count,
                   uint64_t cache_size);
 
     virtual void Serialize(base::Pickle* pickle) const;
     bool Deserialize(base::PickleIterator* it);
 
     bool CheckIndexMetadata();
 
     SimpleIndex::IndexWriteToDiskReason reason() const { return reason_; }
     uint64_t entry_count() const { return entry_count_; }
+    bool has_memory_entry_data() const { return version_ >= 8; }
 
    private:
     FRIEND_TEST_ALL_PREFIXES(IndexMetadataTest, Basics);
     FRIEND_TEST_ALL_PREFIXES(IndexMetadataTest, Serialize);
     FRIEND_TEST_ALL_PREFIXES(IndexMetadataTest, ReadV6Format);
     friend class V6IndexMetadataForTest;
 
     uint64_t magic_number_;
     uint32_t version_;
     SimpleIndex::IndexWriteToDiskReason reason_;
@@ skipping 114 matching lines @@
   static const char kIndexFileName[];
   static const char kTempIndexFileName[];
 
   DISALLOW_COPY_AND_ASSIGN(SimpleIndexFile);
 };
 
 
 }  // namespace disk_cache
 
 #endif  // NET_DISK_CACHE_SIMPLE_SIMPLE_INDEX_FILE_H_