Add ConstThreadState to mach_extensions.h and use it everywhere

client/simulate_crash_mac.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 52 matching lines @@
                       bool set_state) {
   kern_return_t kr;
 
   bool handler_wants_state = ExceptionBehaviorHasState(handler.behavior);
   if (!handler_wants_state) {
     // Regardless of the passed-in value of |set_state|, if the handler won’t be
     // dealing with any state at all, no state should be set.
     set_state = false;
   }
 
-  // A const version of thread_state_t.
-  using ConstThreadState = const natural_t*;
-
   // old_state is only used if the context already captured doesn’t match (or
   // can’t be converted to) what’s registered for the handler.
   thread_state_data_t old_state;
 
   thread_state_flavor_t flavor = handler.flavor;
   ConstThreadState state;
   mach_msg_type_number_t state_count;
   switch (flavor) {
 #if defined(ARCH_CPU_X86_FAMILY)
     case x86_THREAD_STATE:
@@ skipping 149 matching lines @@
                                    false);
       }
     }
   }
 
   LOG_IF(WARNING, !success)
       << "SimulateCrash did not find an appropriate exception handler";
 }
 
 }  // namespace crashpad