[Mac] Remove base::LaunchSynchronize and rewrite content::MachBroker.

base/mac/scoped_mach_port.cc

 // 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.
 
 #include "base/mac/scoped_mach_port.h"
 
 namespace base {
 namespace mac {
 
 ScopedMachPort::ScopedMachPort(mach_port_t port) : port_(port) {
 }
 
 ScopedMachPort::~ScopedMachPort() {
+  reset();
+}
+
+void ScopedMachPort::reset(mach_port_t port) {
   if (port_ != MACH_PORT_NULL) {
     mach_port_deallocate(mach_task_self(), port_);
   }
+  port_ = port;
 }
 
 }  // namespace mac
 }  // namespace base