[SimpleCache] Prefetch stream 1 so that the first read is faster

net/disk_cache/simple/simple_entry_impl.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_IMPL_H_
 #define NET_DISK_CACHE_SIMPLE_SIMPLE_ENTRY_IMPL_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 373 matching lines @@
   // Unlike other streams, stream 0 data is read from the disk when the entry is
   // opened, and then kept in memory. All read/write operations on stream 0
   // affect the |stream_0_data_| buffer. When the entry is closed,
   // |stream_0_data_| is written to the disk.
   // Stream 0 is kept in memory because it is stored in the same file as stream
   // 1 on disk, to reduce the number of file descriptors and save disk space.
   // This strategy allows stream 1 to change size easily. Since stream 0 is only
   // used to write HTTP headers, the memory consumption of keeping it in memory
   // is acceptable.
   scoped_refptr<net::GrowableIOBuffer> stream_0_data_;
+
+  // Some stream 1 data is prefetched when stream 0 is first read, to make the
+  // first read call on stream 1 synchronous. If a write to any stream occurs
+  // on the entry the prefetch buffer is no longer used.
+  scoped_refptr<net::GrowableIOBuffer> stream_1_prefetch_data_;
 };
 
 }  // namespace disk_cache
 
 #endif  // NET_DISK_CACHE_SIMPLE_SIMPLE_ENTRY_IMPL_H_