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

net/disk_cache/simple/simple_synchronous_entry.cc

 // 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.
 
 #include "net/disk_cache/simple/simple_synchronous_entry.h"
 
 #include <algorithm>
 #include <cstring>
 #include <functional>
 #include <limits>
@@ skipping 1481 matching lines @@
   if (header_read_result != sizeof(header)) {
     DLOG(WARNING) << "Could not read header from sparse file.";
     return false;
   }
 
   if (header.initial_magic_number != kSimpleInitialMagicNumber) {
     DLOG(WARNING) << "Sparse file magic number did not match.";
     return false;
   }
 
-  if (header.version != kSimpleVersion) {
+  if (header.version < kLastCompatSparseVersion ||
+      header.version > kSimpleVersion) {
     DLOG(WARNING) << "Sparse file unreadable version.";
     return false;
   }
 
   sparse_ranges_.clear();
 
   int64_t range_header_offset = sizeof(header) + key_.size();
   while (1) {
     SimpleFileSparseRangeHeader range_header;
     int range_header_read_result =
@@ skipping 138 matching lines @@
   range.offset = offset;
   range.length = len;
   range.data_crc32 = data_crc32;
   range.file_offset = data_file_offset;
   sparse_ranges_.insert(std::make_pair(offset, range));
 
   return true;
 }
 
 }  // namespace disk_cache