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 347ec98609128c5301e9db4a51b1f516859fd8ad..01dcb1d0d5971d4d5fc69320a263517809ce5598 100644
--- a/src/platform-macos.cc
+++ b/src/platform-macos.cc
@@ -824,8 +824,9 @@ class SamplerThread : public Thread {
 
   void SampleContext(Sampler* sampler) {
     thread_act_t profiled_thread = sampler->platform_data()->profiled_thread();
+    TickSample sample_obj;
     TickSample* sample = CpuProfiler::StartTickSampleEvent(sampler->isolate());
-    if (sample == NULL) return;
+    if (sample == NULL) sample = &sample_obj;
 
     if (KERN_SUCCESS != thread_suspend(profiled_thread)) return;
 
@@ -934,4 +935,12 @@ void Sampler::Stop() {
 }
 
 
+void Sampler::StartSampling() {
+}
+
+
+void Sampler::StopSampling() {
+}
+
+
 } }  // namespace v8::internal