[turbofan] Add a mutex for recording compilation statistics

src/compilation-statistics.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_COMPILATION_STATISTICS_H_
 #define V8_COMPILATION_STATISTICS_H_
 
 #include <map>
 #include <string>
 
@@ skipping 62 matching lines @@
   friend std::ostream& operator<<(std::ostream& os,
                                   const AsPrintableStatistics& s);
 
   typedef OrderedStats PhaseKindStats;
   typedef std::map<std::string, PhaseKindStats> PhaseKindMap;
   typedef std::map<std::string, PhaseStats> PhaseMap;
 
   TotalStats total_stats_;
   PhaseKindMap phase_kind_map_;
   PhaseMap phase_map_;
+  base::Mutex record_mutex_;
 
   DISALLOW_COPY_AND_ASSIGN(CompilationStatistics);
 };
 
 std::ostream& operator<<(std::ostream& os, const AsPrintableStatistics& s);
 
 }  // namespace internal
 }  // namespace v8
 
 #endif