Take instrumentation overhead into account when plotting.

src/counters.cc

Index: src/counters.cc
diff --git a/src/counters.cc b/src/counters.cc
index e152c752f7adbd0acf9cc64c9d00d2709fef0918..6d453d6aa3490ba20c0d62976aafe72392834b73 100644
--- a/src/counters.cc
+++ b/src/counters.cc
@@ -77,7 +77,7 @@ void* Histogram::CreateHistogram() const {
 
 // Start the timer.
 void HistogramTimer::Start() {
-  if (histogram_.Enabled() || FLAG_log_timer_events) {
+  if (histogram_.Enabled() || FLAG_log_internal_timer_events) {
     stop_time_ = 0;
     start_time_ = OS::Ticks();
   }
@@ -91,7 +91,7 @@ void HistogramTimer::Stop() {
     int milliseconds = static_cast<int>(stop_time_ - start_time_) / 1000;
     histogram_.AddSample(milliseconds);
   }
-  if (FLAG_log_timer_events) {
+  if (FLAG_log_internal_timer_events) {
     LOG(Isolate::Current(),
         TimerEvent(histogram_.name_, start_time_, OS::Ticks()));
   }