Replacing circular queue by single buffer in CPU Profiler.

src/platform-macos.cc

Index: src/platform-macos.cc
diff --git a/src/platform-macos.cc b/src/platform-macos.cc
index 704fe12619c8ce7cc51f4d8ce5bb793b21cd5a8a..a570868e51fab61671cc3e5c78126b35ec5153d8 100644
--- a/src/platform-macos.cc
+++ b/src/platform-macos.cc
@@ -819,9 +819,8 @@ class SamplerThread : public Thread {
 
   void SampleContext(Sampler* sampler) {
     thread_act_t profiled_thread = sampler->platform_data()->profiled_thread();
-    TickSample sample_obj;
-    TickSample* sample = CpuProfiler::TickSampleEvent(sampler->isolate());
-    if (sample == NULL) sample = &sample_obj;
+    TickSample* sample = CpuProfiler::StartTickSampleEvent(sampler->isolate());
+    if (sample == NULL) return;
 
     if (KERN_SUCCESS != thread_suspend(profiled_thread)) return;
 
@@ -858,6 +857,7 @@ class SamplerThread : public Thread {
       sampler->SampleStack(sample);
       sampler->Tick(sample);
     }
+    CpuProfiler::FinishTickSampleEvent(sampler->isolate());
     thread_resume(profiled_thread);
   }