Add NewMachPort() and its test, and switch call sites to use it

util/test/mac/mach_multiprocess.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 197 matching lines @@
   info_->remote_port.reset();
   info_->local_port.reset();
 }
 
 void MachMultiprocess::MultiprocessChild() {
   ScopedForbidReturn forbid_return;;
 
   // local_port is not valid in the forked child process.
   ignore_result(info_->local_port.release());
 
-  mach_port_t local_port;
-  kern_return_t kr = mach_port_allocate(
-      mach_task_self(), MACH_PORT_RIGHT_RECEIVE, &local_port);
-  ASSERT_EQ(KERN_SUCCESS, kr) << MachErrorMessage(kr, "mach_port_allocate");
-  info_->local_port.reset(local_port);
+  info_->local_port.reset(NewMachPort(MACH_PORT_RIGHT_RECEIVE));
+  ASSERT_NE(kMachPortNull, info_->local_port);
 
   // The remote port can be obtained from the bootstrap server.
   mach_port_t remote_port;
-  kr = bootstrap_look_up(
+  kern_return_t kr = bootstrap_look_up(
       bootstrap_port, info_->service_name.c_str(), &remote_port);
   ASSERT_EQ(BOOTSTRAP_SUCCESS, kr)
       << BootstrapErrorMessage(kr, "bootstrap_look_up");
   info_->remote_port.reset(remote_port);
 
   // The “hello” message will provide the parent with its remote port, a send
   // right to the child task’s local port receive right. It will also carry a
   // send right to the child task’s task port.
   SendHelloMessage message = {};
   message.header.msgh_bits =
@@ skipping 33 matching lines @@
   if (testing::Test::HasFailure()) {
     // Trigger the ScopedForbidReturn destructor.
     return;
   }
 
   forbid_return.Disarm();
 }
 
 }  // namespace test
 }  // namespace crashpad