Add SimpleCache index file heuristics

net/disk_cache/simple/simple_index_file.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_index_file.h"
 
 #include "base/file_util.h"
 #include "base/hash.h"
 #include "base/logging.h"
 #include "base/pickle.h"
@@ skipping 143 matching lines @@
     LOG(ERROR) << "Could not write Simple Cache index to temporary file: "
                << temp_filename.value();
     file_util::Delete(temp_filename, /* recursive = */ false);
     return;
   }
   // Swap temp and index_file.
   bool result = file_util::ReplaceFile(temp_filename, index_filename);
   DCHECK(result);
 }
 
+// static
+bool SimpleIndexFile::IndexFileIsStale(const base::FilePath& index_filename) {
+  base::PlatformFileInfo dir_info;
+  base::PlatformFileInfo index_info;
+  if (!file_util::GetFileInfo(index_filename.DirName(), &dir_info))
+    return false;
+  DCHECK(dir_info.is_directory);
+  if (!file_util::GetFileInfo(index_filename, &index_info))
+    return false;
+
+  // Index file last_modified must be equal to the directory last_modified since
+  // the last operation we do is ReplaceFile in the
+  // SimpleIndexFile::WriteToDisk().
+  // If not true, we need to restore the index.
+  return index_info.last_modified != dir_info.last_modified;

[gavinp, 2013/04/19 09:30:17]

I think index_info.last_modified >= dir_info.last_modified is better. Right now
we do an atomic rename to put the index in place so equality should be right,
but other operations can update file mtime without changing directory mtime (for
instance, mutating a file).

[felipeg, 2013/04/19 10:14:05]

Done.

+}
+
 }  // namespace disk_cache