Make synchronous methods on disk_cache::SimpleEntryImpl() reentrant.

net/disk_cache/simple/simple_disk_format.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_DISK_FORMAT_H_
 #define NET_DISK_CACHE_SIMPLE_SIMPLE_DISK_FORMAT_H_
 
 namespace disk_cache {
 
 const uint64 kSimpleInitialMagicNumber = 0xfcfb6d1ba7725c30;
 
 // A file in the Simple cache consists of a SimpleFileHeader followed
 // by data.
 
 const uint32 kSimpleVersion = 1;
 
+static const int kSimpleEntryFileCount = 3;

[pasko-google - do not use, 2013/02/12 14:15:10]

nit: a better name would be kSimpleEntryStreamCount because the SimpleEntryImpl
is abstracted away enough from the implementation detail that streams are
written into separate files in the synchronous entry.

By the way, why is it SimpleEntryImpl and not a more human language name
SimpleCacheEntry?

+
 struct SimpleFileHeader {
   uint64 initial_magic_number;
   uint32 version;
   uint32 key_length;
   uint32 key_hash;
 };
 
 }  // namespace disk_cache
 
 #endif  // NET_DISK_CACHE_SIMPLE_SIMPLE_DISK_FORMAT_H_