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

net/disk_cache/simple/simple_version_upgrade.cc

 // Copyright 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_version_upgrade.h"
 
 #include <cstring>
 
 #include "base/files/file.h"
 #include "base/files/file_path.h"
@@ skipping 180 matching lines @@
       return false;
     }
     version_from++;
   }
   DCHECK_LE(6U, version_from);
   if (version_from == 6) {
     // No upgrade from V6 -> V7, because the entry format has not changed and
     // the V7 index reader is backwards compatible.
     version_from++;
   }
+
+  if (version_from == 7) {
+    // Likewise, V7 -> V8 is handled entirely by the index reader.
+    version_from++;
+  }
+
   DCHECK_EQ(kSimpleVersion, version_from);
 
   if (!new_fake_index_needed)
     return true;
 
   const base::FilePath temp_fake_index = path.AppendASCII("upgrade-index");
   if (!WriteFakeIndexFile(temp_fake_index, experiment)) {
     base::DeleteFile(temp_fake_index, /* recursive = */ false);
     LOG(ERROR) << "Failed to write a new fake index.";
     LogMessageFailedUpgradeFromVersion(file_header.version);
     return false;
   }
   if (!base::ReplaceFile(temp_fake_index, fake_index, NULL)) {
     LOG(ERROR) << "Failed to replace the fake index.";
     LogMessageFailedUpgradeFromVersion(file_header.version);
     return false;
   }
   return true;
 }
 
 }  // namespace disk_cache