Add message sizing to basic IPC traits and struct macros.

ipc/ipc_message_macros.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.
 
 // Defining IPC Messages
 //
 // Your IPC messages will be defined by macros inside of an XXX_messages.h
 // header file.  Most of the time, the system can automatically generate all
 // of messaging mechanism from these definitions, but sometimes some manual
 // coding is required.  In these cases, you will also have an XXX_messages.cc
@@ skipping 27 matching lines @@
 // the following code:
 //     // Get basic type definitions.
 //     #define IPC_MESSAGE_IMPL
 //     #include "path/to/YYY_message_generator.h"
 //     // Generate constructors.
 //     #include "ipc/struct_constructor_macros.h"
 //     #include "path/to/YYY_message_generator.h"
 //     // Generate destructors.
 //     #include "ipc/struct_destructor_macros.h"
 //     #include "path/to/YYY_message_generator.h"
+//     // Generate param traits size methods.
+//     #include "ipc/param_traits_size_macros.h"
+//     namespace IPC {
+//     #include "path/to/YYY_message_generator.h"
+//     }  // namespace IPC
 //     // Generate param traits write methods.
 //     #include "ipc/param_traits_write_macros.h"
 //     namespace IPC {
 //     #include "path/to/YYY_message_generator.h"
 //     }  // namespace IPC
 //     // Generate param traits read methods.
 //     #include "ipc/param_traits_read_macros.h"
 //     namespace IPC {
 //     #include "path/to/YYY_message_generator.h"
 //     }  // namespace IPC
@@ skipping 917 matching lines @@
 // This corresponds to an enum value from IPCMessageStart.
 #define IPC_MESSAGE_CLASS(message) \
   IPC_MESSAGE_ID_CLASS(message.type())
 
 #endif  // IPC_IPC_MESSAGE_MACROS_H_
 
 // Clean up IPC_MESSAGE_START in this unguarded section so that the
 // XXX_messages.h files need not do so themselves.  This makes the
 // XXX_messages.h files easier to write.
 #undef IPC_MESSAGE_START