Add ConstThreadState to mach_extensions.h and use it everywhere

tools/mac/catch_exception_tool.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 50 matching lines @@
   // UniversalMachExcServer::Interface:
   virtual 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;
     ++*exceptions_handled_;
 
     fprintf(options_.file,
             "%s: behavior %s, ",
@@ skipping 222 matching lines @@
 
   return EXIT_SUCCESS;
 }
 
 }  // namespace
 }  // namespace crashpad
 
 int main(int argc, char* argv[]) {
   return crashpad::CatchExceptionToolMain(argc, argv);
 }