Fix data race in SamplingCircularQueue

src/cpu-profiler.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 92 matching lines @@
 
   INLINE(void UpdateCodeMap(CodeMap* code_map));
 };
 
 
 class TickSampleEventRecord {
  public:
   // The parameterless constructor is used when we dequeue data from
   // the ticks buffer.
   TickSampleEventRecord() { }
-  explicit TickSampleEventRecord(unsigned order)
-      : filler(1),
-        order(order) {
-    ASSERT(filler != SamplingCircularQueue::kClear);
-  }
+  explicit TickSampleEventRecord(unsigned order) : order(order) { }
 
-  // The first machine word of a TickSampleEventRecord must not ever
-  // become equal to SamplingCircularQueue::kClear.  As both order and
-  // TickSample's first field are not reliable in this sense (order
-  // can overflow, TickSample can have all fields reset), we are
-  // forced to use an artificial filler field.
-  int filler;
   unsigned order;
   TickSample sample;
 
   static TickSampleEventRecord* cast(void* value) {
     return reinterpret_cast<TickSampleEventRecord*>(value);
   }
 };
 
 
 class CodeEventsContainer {
@@ skipping 134 matching lines @@
   bool is_profiling_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(CpuProfiler);
 };
 
 } }  // namespace v8::internal
 
 
 #endif  // V8_CPU_PROFILER_H_