Pass Mach message trailers to server handler functions

util/mach/mach_message_util_test.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 45 matching lines @@
   EXPECT_EQ(NDR_record.char_rep, reply.NDR.char_rep);
   EXPECT_EQ(NDR_record.float_rep, reply.NDR.float_rep);
   EXPECT_EQ(NDR_record.reserved2, reply.NDR.reserved2);
   EXPECT_EQ(MIG_TYPE_ERROR, reply.RetCode);
 
   SetMIGReplyError(&reply.Head, MIG_BAD_ID);
 
   EXPECT_EQ(MIG_BAD_ID, reply.RetCode);
 }
 
+TEST(MachMessageUtil, MachMessageTrailerFromHeader) {
+  mach_msg_empty_t empty;
+  empty.send.header.msgh_size = sizeof(mach_msg_empty_send_t);
+  EXPECT_EQ(&empty.rcv.trailer,
+            MachMessageTrailerFromHeader(&empty.rcv.header));
+
+  struct TestSendMessage : public mach_msg_header_t {
+    uint8_t data[126];
+  };
+  struct TestReceiveMessage : public TestSendMessage {
+    mach_msg_trailer_t trailer;
+  };
+  union TestMessage {
+    TestSendMessage send;
+    TestReceiveMessage receive;
+  };
+
+  TestMessage test;
+  test.send.msgh_size = sizeof(TestSendMessage);
+  EXPECT_EQ(&test.receive.trailer,
+            MachMessageTrailerFromHeader(&test.receive));
+}
+
 }  // namespace
 }  // namespace test
 }  // namespace crashpad