Take instrumentation overhead into account when plotting.

src/log.h

Index: src/log.h
diff --git a/src/log.h b/src/log.h
index 12dc9231a009443f172e43d63a88a6d64b86e400..5fab4facd1a59718822fb5fcb9631c012d77afd8 100644
--- a/src/log.h
+++ b/src/log.h
@@ -287,11 +287,11 @@ class Logger {
    public:
     TimerEventScope(Isolate* isolate, const char* name)
         : isolate_(isolate), name_(name), start_(0) {
-      if (FLAG_log_timer_events) start_ = OS::Ticks();
+      if (FLAG_log_internal_timer_events) start_ = OS::Ticks();
     }
 
     ~TimerEventScope() {
-      if (FLAG_log_timer_events) LogTimerEvent();
+      if (FLAG_log_internal_timer_events) LogTimerEvent();
     }
 
     void LogTimerEvent();