Pass Mach message trailers to server handler functions

util/mach/mach_message_util.cc

 // Copyright 2014 The Crashpad Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 16 matching lines @@
   reinterpret_cast<mig_reply_error_t*>(out_header)->NDR = NDR_record;
 
   // MIG-generated dispatch routines don’t do this, but they should.
   out_header->msgh_reserved = 0;
 }
 
 void SetMIGReplyError(mach_msg_header_t* out_header, kern_return_t error) {
   reinterpret_cast<mig_reply_error_t*>(out_header)->RetCode = error;
 }
 
+const mach_msg_trailer_t* MachMessageTrailerFromHeader(
+    const mach_msg_header_t* header) {
+  vm_address_t header_address = reinterpret_cast<vm_address_t>(header);
+  vm_address_t trailer_address = header_address + round_msg(header->msgh_size);
+  return reinterpret_cast<const mach_msg_trailer_t*>(trailer_address);
+}
+
 }  // namespace crashpad