Include implicit_cast.h at all users of it.

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 13 matching lines @@
 #include "base/logging.h"
 #include "base/mac/scoped_mach_port.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/rand_util.h"
 #include "gtest/gtest.h"
 #include "test/errors.h"
 #include "test/mac/mach_errors.h"
 #include "util/file/file_io.h"
 #include "util/mach/mach_extensions.h"
 #include "util/mach/mach_message.h"
+#include "util/misc/implicit_cast.h"
 #include "util/misc/scoped_forbid_return.h"
 
 namespace {
 
 // The “hello” message contains a send right to the child process’ task port.
 struct SendHelloMessage : public mach_msg_base_t {
   mach_msg_port_descriptor_t port_descriptor;
 };
 
 struct ReceiveHelloMessage : public SendHelloMessage {
@@ skipping 227 matching lines @@
   if (testing::Test::HasFailure()) {
     // Trigger the ScopedForbidReturn destructor.
     return;
   }
 
   forbid_return.Disarm();
 }
 
 }  // namespace test
 }  // namespace crashpad