Avoid cross thread malloc / free pair of IOBuffer on the simple cache

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 235 matching lines @@
 
   // Called after an asynchronous read. Updates |crc32s_| if possible.
   void ReadOperationComplete(int stream_index,
                              int offset,
                              const CompletionCallback& completion_callback,
                              std::unique_ptr<uint32_t> read_crc32,
                              std::unique_ptr<SimpleEntryStat> entry_stat,
                              std::unique_ptr<int> result);
 
   // Called after an asynchronous write completes.
+  // |buf| parameter brings back a reference to net::IOBuffer to the original
+  // thread, so that we can reduce cross thread malloc/free pair.
+  // See http://crbug.com/708644 for details.
   void WriteOperationComplete(int stream_index,
                               const CompletionCallback& completion_callback,
                               std::unique_ptr<SimpleEntryStat> entry_stat,
-                              std::unique_ptr<int> result);
+                              std::unique_ptr<int> result,
+                              net::IOBuffer* buf);
 
   void ReadSparseOperationComplete(
       const CompletionCallback& completion_callback,
       std::unique_ptr<base::Time> last_used,
       std::unique_ptr<int> result);
 
   void WriteSparseOperationComplete(
       const CompletionCallback& completion_callback,
       std::unique_ptr<SimpleEntryStat> entry_stat,
       std::unique_ptr<int> result);
@@ skipping 115 matching lines @@
   // 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_;
 };
 
 }  // namespace disk_cache
 
 #endif  // NET_DISK_CACHE_SIMPLE_SIMPLE_ENTRY_IMPL_H_