Add StartProfiling to filter out v8 warm up

src/profiler/cpu-profiler.cc

Index: src/profiler/cpu-profiler.cc
diff --git a/src/profiler/cpu-profiler.cc b/src/profiler/cpu-profiler.cc
index cff8c79955a1057e2a454fffa698702546486712..80d488f12c527ff276dfd9562c75a4de7468980f 100644
--- a/src/profiler/cpu-profiler.cc
+++ b/src/profiler/cpu-profiler.cc
@@ -300,6 +300,7 @@ void CpuProfiler::CollectSample() {
 
 void CpuProfiler::StartProfiling(const char* title, bool record_samples) {
   if (profiles_->StartProfiling(title, record_samples)) {
+    TRACE_EVENT0("v8", "CpuProfiler::StartProfiling");
     StartProcessorIfNotStarted();
   }
 }