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

src/log.cc

Index: src/log.cc
diff --git a/src/log.cc b/src/log.cc
index efbb8f7f57f7150efda8615b54f9cdf2922b9692..4a53db4d8dd6295fdb2a71bbfaf14a5ad45dd277 100644
--- a/src/log.cc
+++ b/src/log.cc
@@ -633,46 +633,30 @@ void Logger::SharedLibraryEvent(const wchar_t* library_path,
 }
 
 
-void Logger::TimerEvent(const char* name, int64_t start, int64_t end) {
+void Logger::TimerEvent(StartEnd se, const char* name) {
   if (!log_->IsEnabled()) return;
   ASSERT(FLAG_log_internal_timer_events);
   LogMessageBuilder msg(this);
-  int since_epoch = static_cast<int>(start - epoch_);
-  int pause_time = static_cast<int>(end - start);
-  msg.Append("timer-event,\"%s\",%ld,%ld\n", name, since_epoch, pause_time);
+  int since_epoch = static_cast<int>(OS::Ticks() - epoch_);
+  const char* format = (se == START) ? "timer-event-start,\"%s\",%ld\n"
+                                     : "timer-event-end,\"%s\",%ld\n";
+  msg.Append(format, name, since_epoch);
   msg.WriteToLogFile();
 }
 
 
-void Logger::ExternalSwitch(StateTag old_tag, StateTag new_tag) {
-  if (old_tag != EXTERNAL && new_tag == EXTERNAL) {
-    enter_external_ = OS::Ticks();
-  }
-  if (old_tag == EXTERNAL && new_tag != EXTERNAL && enter_external_ != 0) {
-    TimerEvent("V8.External", enter_external_, OS::Ticks());
-    enter_external_ = 0;
-  }
-}
-
-
 void Logger::EnterExternal() {
-  LOGGER->enter_external_ = OS::Ticks();
+  LOG(ISOLATE, TimerEvent(START, TimerEventScope::v8_external));
 }
 
 
 void Logger::LeaveExternal() {
-  if (enter_external_ == 0) return;
-  Logger* logger = LOGGER;
-  logger->TimerEvent("V8.External", enter_external_, OS::Ticks());
-  logger->enter_external_ = 0;
+  LOG(ISOLATE, TimerEvent(END, TimerEventScope::v8_external));
 }
 
 
-int64_t Logger::enter_external_ = 0;
-
-
-void Logger::TimerEventScope::LogTimerEvent() {
-  LOG(isolate_, TimerEvent(name_, start_, OS::Ticks()));
+void Logger::TimerEventScope::LogTimerEvent(StartEnd se) {
+  LOG(isolate_, TimerEvent(se, name_));
 }
 
 
@@ -683,6 +667,7 @@ const char* Logger::TimerEventScope::v8_recompile_parallel =
 const char* Logger::TimerEventScope::v8_compile_full_code =
     "V8.CompileFullCode";
 const char* Logger::TimerEventScope::v8_execute = "V8.Execute";
+const char* Logger::TimerEventScope::v8_external = "V8.External";
 
 
 void Logger::LogRegExpSource(Handle<JSRegExp> regexp) {