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

src/cpu-profiler.cc

Index: src/cpu-profiler.cc
diff --git a/src/cpu-profiler.cc b/src/cpu-profiler.cc
index 8f72c1755cb898264e4d2a5ba029ebc77b019f09..08c82db2397b963cc72bc7f5190c44c97bc48292 100644
--- a/src/cpu-profiler.cc
+++ b/src/cpu-profiler.cc
@@ -519,6 +519,7 @@ void CpuProfiler::StartProcessorIfNotStarted() {
       sampler->Start();
       need_to_stop_sampler_ = true;
     }
+    sampler->SetHasProcessingThread(true);
     sampler->IncreaseProfilingDepth();
     processor_->Start();
   }
@@ -561,6 +562,7 @@ void CpuProfiler::StopProcessor() {
   Logger* logger = Isolate::Current()->logger();
   Sampler* sampler = logger->sampler();
   sampler->DecreaseProfilingDepth();
+  sampler->SetHasProcessingThread(false);
   if (need_to_stop_sampler_) {
     sampler->Stop();
     need_to_stop_sampler_ = false;