Add ConstThreadState to mach_extensions.h and use it everywhere

client/simulate_crash_mac_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 70 matching lines @@
 
   // UniversalMachExcServer::Interface:
   kern_return_t CatchMachException(exception_behavior_t behavior,
                                    exception_handler_t exception_port,
                                    thread_t thread,
                                    task_t task,
                                    exception_type_t exception,
                                    const mach_exception_data_type_t* code,
                                    mach_msg_type_number_t code_count,
                                    thread_state_flavor_t* flavor,
-                                   const natural_t* old_state,
+                                   ConstThreadState old_state,
                                    mach_msg_type_number_t old_state_count,
                                    thread_state_t new_state,
                                    mach_msg_type_number_t* new_state_count,
                                    const mach_msg_trailer_t* trailer,
                                    bool* destroy_complex_request) override {
     *destroy_complex_request = true;
 
     // Check the entire exception message, because most or all of it was
     // generated by SimulateCrash() instead of the kernel.
 
@@ skipping 275 matching lines @@
           test_simulate_crash_mac.Run();
         }
       }
     }
   }
 }
 
 }  // namespace
 }  // namespace test
 }  // namespace crashpad