Log event start and event end separately when using --log-timer-events.

tools/plot-timer-events

 #!/bin/sh
 
 # find the name of the log file to process, it must not start with a dash.
 log_file="v8.log"
 for arg in "$@"
 do
   if ! expr "X${arg}" : "^X-" > /dev/null; then
     log_file=${arg}
   fi
 done
@@ skipping 23 matching lines @@
 
 if [ -n "$DISTORTION" ]; then
   distortion=$DISTORTION
 else
   # Try to find out how much the instrumentation overhead is.
   calibration_log=calibration.log
   calibration_script="for (var i = 0; i < 1000000; i++) print();"
 
   $d8_exec --nocrankshaft --prof --logfile $calibration_log \
        --log-timer-events -e "$calibration_script" > /dev/null
-  t_1=`grep "V8.Execute" $calibration_log  | tail -n1 | awk -F, '{print $4}'`
-  n_1=`grep "timer-event" $calibration_log  | wc -l`
+  t_1_start=`grep "timer-event-start,\"V8.Execute\"" $calibration_log  \
+       | tail -n1 | awk -F, '{print $3}'`
+  t_1_end=`grep "timer-event-end,\"V8.Execute\"" $calibration_log  \
+       | tail -n1 | awk -F, '{print $3}'`
+  n_1=`grep "timer-event\|tick" $calibration_log  | wc -l`
 
   $d8_exec --nocrankshaft --prof --logfile $calibration_log \
        --log-internal-timer-events -e "$calibration_script" > /dev/null
-  t_2=`grep "V8.Execute" $calibration_log  | tail -n1 | awk -F, '{print $4}'`
-  n_2=`grep "timer-event" $calibration_log  | wc -l`
+  t_2_start=`grep "timer-event-start,\"V8.Execute\"" $calibration_log  \
+       | tail -n1 | awk -F, '{print $3}'`
+  t_2_end=`grep "timer-event-end,\"V8.Execute\"" $calibration_log  \
+       | tail -n1 | awk -F, '{print $3}'`
+  n_2=`grep "timer-event\|tick" $calibration_log  | wc -l`
 
   rm $calibration_log
 
   # Overhead in picoseconds.
-  distortion=`echo "1000*($t_1 - $t_2)/($n_1 - $n_2)" | bc`
+  distortion=`echo "1000*(($t_1_end - $t_1_start) - ($t_2_end - $t_2_start)) \
+                    / ($n_1 - $n_2)" | bc`
 fi
 
 if [ -n "$PLOT_RANGE" ]; then
   plot_range=$PLOT_RANGE
 else
   plot_range=auto,auto
 fi
 
 echo "DISTORTION=$distortion"
 echo "PLOT_RANGE=$plot_range"
 
 echo -e "plot-range,$plot_range\ndistortion,$distortion" | cat - $log_file |
     $d8_exec $tools_path/csvparser.js \
     $tools_path/splaytree.js $tools_path/codemap.js \
     $tools_path/logreader.js $tools_path/plot-timer-events.js \
     2>/dev/null | gnuplot > timer-events.png