Add new simple disk cache backend.

net/disk_cache/simple/simple_disk_format.h

Index: net/disk_cache/simple/simple_disk_format.h
diff --git a/net/disk_cache/simple/simple_disk_format.h b/net/disk_cache/simple/simple_disk_format.h
new file mode 100644
index 0000000000000000000000000000000000000000..3ee6bef99db9f327e3dfe817c37f058d708bbfe9
--- /dev/null
+++ b/net/disk_cache/simple/simple_disk_format.h
@@ -0,0 +1,26 @@
+// 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_
+
+namespace disk_cache {
+
+const uint64 kSimpleInitialMagicNumber = 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_