Add ConstThreadState to mach_extensions.h and use it everywhere

snapshot/mac/exception_snapshot_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 27 matching lines @@
 
 ExceptionSnapshotMac::~ExceptionSnapshotMac() {
 }
 
 bool ExceptionSnapshotMac::Initialize(ProcessReader* process_reader,
                                       thread_t exception_thread,
                                       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* state,
+                                      ConstThreadState state,
                                       mach_msg_type_number_t state_count) {
   INITIALIZATION_STATE_SET_INITIALIZING(initialized_);
 
   codes_.push_back(exception);
   for (mach_msg_type_number_t code_index = 0;
        code_index < code_count;
        ++code_index) {
     codes_.push_back(code[code_index]);
   }
 
@@ skipping 107 matching lines @@
   return exception_address_;
 }
 
 const std::vector<uint64_t>& ExceptionSnapshotMac::Codes() const {
   INITIALIZATION_STATE_DCHECK_VALID(initialized_);
   return codes_;
 }
 
 }  // namespace internal
 }  // namespace crashpad