Rollback of r11015, r11014, r11011, r11010 in trunk branch.

src/log.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 436 matching lines @@
 
   // Adds/Removes an active sampler.
   static void AddActiveSampler(Sampler* sampler);
   static void RemoveActiveSampler(Sampler* sampler);
 
  private:
   static bool ActiveSamplersExist() {
     return active_samplers_ != NULL && !active_samplers_->is_empty();
   }
 
+  static Mutex* mutex_;  // Protects the state below.
   static List<Sampler*>* active_samplers_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(SamplerRegistry);
 };
 
 
 // Class that extracts stack trace, used for profiling.
 class StackTracer : public AllStatic {
  public:
   static void Trace(Isolate* isolate, TickSample* sample);
 };
 
 } }  // namespace v8::internal
 
 
 #endif  // V8_LOG_H_