Perform CPU sampling by CPU sampling thread only iff processing thread is not running.

src/platform-macos.cc

Index: src/platform-macos.cc
diff --git a/src/platform-macos.cc b/src/platform-macos.cc
index a570868e51fab61671cc3e5c78126b35ec5153d8..5eff46200cb458117df882e80857031c64169ef7 100644
--- a/src/platform-macos.cc
+++ b/src/platform-macos.cc
@@ -819,8 +819,10 @@ class SamplerThread : public Thread {
 
   void SampleContext(Sampler* sampler) {
     thread_act_t profiled_thread = sampler->platform_data()->profiled_thread();
-    TickSample* sample = CpuProfiler::StartTickSampleEvent(sampler->isolate());
-    if (sample == NULL) return;
+    TickSample sample_obj;
+    TickSample* sample = CpuProfiler::StartTickSampleEvent(isolate);
+    if (sample == NULL) sample = &sample_obj;
+
 
     if (KERN_SUCCESS != thread_suspend(profiled_thread)) return;
 
@@ -929,4 +931,12 @@ void Sampler::Stop() {
 }
 
 
+void Sampler::StartSampling() {
+}
+
+
+void Sampler::StopSampling() {
+}
+
+
 } }  // namespace v8::internal