SimpleCache: open with fewer seeks.

net/disk_cache/simple/simple_entry_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_ENTRY_FORMAT_H_
 #define NET_DISK_CACHE_SIMPLE_SIMPLE_ENTRY_FORMAT_H_
 
 #include <stdint.h>
 
 #include "net/base/net_export.h"
@@ skipping 29 matching lines @@
 
   uint64_t initial_magic_number;
   uint32_t version;
   uint32_t key_length;
   uint32_t key_hash;
 };
 
 struct NET_EXPORT_PRIVATE SimpleFileEOF {
   enum Flags {
     FLAG_HAS_CRC32 = (1U << 0),
+    FLAG_HAS_KEY_SHA256 = (2U << 1),

[Randy Smith (Not in Mondays), 2016/05/19 19:38:49]

Are you intentionally leaving a gap between the bits?  If so, why?  

This also seems a confusing way to do it; is there a message you're trying to
communicate by how you're setting the bit?

(1U << 0 == 1, 2U << 1 == 4)

[gavinp, 2016/05/20 01:42:31]

Nope, that was a mistake. Thanks.

   };
 
   SimpleFileEOF();
 
   uint64_t final_magic_number;
   uint32_t flags;
   uint32_t data_crc32;
   // |stream_size| is only used in the EOF record for stream 0.
   uint32_t stream_size;
 };
 
 struct SimpleFileSparseRangeHeader {
   SimpleFileSparseRangeHeader();
 
   uint64_t sparse_range_magic_number;
   int64_t offset;
   int64_t length;
   uint32_t data_crc32;
 };
 
 }  // namespace disk_cache
 
 #endif  // NET_DISK_CACHE_SIMPLE_SIMPLE_ENTRY_FORMAT_H_