Add new simple disk cache backend.

net/disk_cache/simple/simple_disk_format.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_DISK_FORMAT_H_
+#define NET_DISK_CACHE_SIMPLE_SIMPLE_DISK_FORMAT_H_
+
+#include "base/port.h"
+
+namespace disk_cache {
+
+const uint64 kSimpleInitialMagicNumber = GG_UINT64_C(0xfcfb6d1ba7725c30);
+
+// A file in the Simple cache consists of a SimpleFileHeader followed
+// by data.
+
+const uint32 kSimpleVersion = 1;
+
+struct SimpleFileHeader {
+  uint64 initial_magic_number;
+  uint32 version;
+  uint32 key_length;
+  uint32 key_hash;
+};
+
+}  // namespace disk_cache
+
+#endif  // NET_DISK_CACHE_SIMPLE_SIMPLE_DISK_FORMAT_H_