Add SimpleCache index file heuristics

net/disk_cache/simple/simple_index.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_INDEX_H_
 #define NET_DISK_CACHE_SIMPLE_SIMPLE_INDEX_H_
 
 #include <map>
 #include <string>
 
@@ skipping 92 matching lines @@
 
   static void InsertInEntrySet(const EntryMetadata& entry_metadata,
                                EntrySet* entry_set);
 
  private:
   typedef base::Callback<void(scoped_ptr<EntrySet>, bool force_index_flush)>
       IndexCompletionCallback;
 
   void PostponeWritingToDisk();
 
+  // Using the mtime of the file and its mtime, detects if the index file is
+  // stale.
+  static bool IsIndexFileStale(const base::FilePath& index_filename);
+
   static void LoadFromDisk(
       const base::FilePath& index_filename,
       base::SingleThreadTaskRunner* io_thread,
       const IndexCompletionCallback& completion_callback);
 
   // Enumerates all entries' files on disk and regenerates the index.
   static scoped_ptr<SimpleIndex::EntrySet> RestoreFromDisk(
       const base::FilePath& index_filename);
 
   static void WriteToDiskInternal(const base::FilePath& index_filename,
@@ skipping 23 matching lines @@
   // Timestamp of the last time we wrote the index to disk.
   // PostponeWritingToDisk() may give up postponing and allow the write if it
   // has been a while since last time we wrote.
   base::Time last_write_to_disk_;
   base::OneShotTimer<SimpleIndex> write_to_disk_timer_;
 };
 
 }  // namespace disk_cache
 
 #endif  // NET_DISK_CACHE_SIMPLE_SIMPLE_INDEX_H_