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

src/platform-nullos.cc

Index: src/platform-nullos.cc
diff --git a/src/platform-nullos.cc b/src/platform-nullos.cc
index 7aaa7b204a3f129b2c1b0eabcba89a46bcb93054..7a378cbc6bb0af09cd224beed0fc46aa9e2fc6f5 100644
--- a/src/platform-nullos.cc
+++ b/src/platform-nullos.cc
@@ -508,4 +508,12 @@ void ProfileSampler::Stop() {
 }
 
 
+void Sampler::StartSampling() {
+}
+
+
+void Sampler::StopSampling() {
+}
+
+
 } }  // namespace v8::internal