Add SimpleCache index file heuristics

net/disk_cache/simple/simple_index_file.cc

Index: net/disk_cache/simple/simple_index_file.cc
diff --git a/net/disk_cache/simple/simple_index_file.cc b/net/disk_cache/simple/simple_index_file.cc
index a2913202276b22ef724a04abb6ffd0cdc34aa419..f5dcd5a9ef711d7fa210d48787203a4ce0f1a255 100644
--- a/net/disk_cache/simple/simple_index_file.cc
+++ b/net/disk_cache/simple/simple_index_file.cc
@@ -161,4 +161,21 @@ void SimpleIndexFile::WriteToDisk(const base::FilePath& 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