Trim IPC ChannelReader's buffer.

ipc/ipc_channel.h

 // Copyright (c) 2012 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 IPC_IPC_CHANNEL_H_
 #define IPC_IPC_CHANNEL_H_
 
 #include <stdint.h>
 
 #include <string>
@@ skipping 79 matching lines @@
     CLOSE_FD_MESSAGE_TYPE = HELLO_MESSAGE_TYPE - 1
   };
 
   // The maximum message size in bytes. Attempting to receive a message of this
   // size or bigger results in a channel error.
   static const size_t kMaximumMessageSize = 128 * 1024 * 1024;
 
   // Amount of data to read at once from the pipe.
   static const size_t kReadBufferSize = 4 * 1024;
 
+  // Maximum persistent read buffer size. Read buffer can grow larger to
+  // accommodate large messages, but it's recommended to shrink back to this
+  // value because it fits 99.9% of all messages (see issue 529940 for data).
+  static const size_t kMaximumReadBufferSize = 64 * 1024;
+
   // Initialize a Channel.
   //
   // |channel_handle| identifies the communication Channel. For POSIX, if
   // the file descriptor in the channel handle is != -1, the channel takes
   // ownership of the file descriptor and will close it appropriately, otherwise
   // it will create a new descriptor internally.
   // |listener| receives a callback on the current thread for each newly
   // received message.
   //
   // There are four type of modes how channels operate:
@@ skipping 140 matching lines @@
 
 #if defined(OS_POSIX)
 // SocketPair() creates a pair of socket FDs suitable for using with
 // IPC::Channel.
 IPC_EXPORT bool SocketPair(int* fd1, int* fd2);
 #endif
 
 }  // namespace IPC
 
 #endif  // IPC_IPC_CHANNEL_H_