Remove V8.External traces due to its high overhead

src/log.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/log.h"
 
 #include <cstdarg>
 #include <sstream>
 
 #include "src/bailout-reason.h"
@@ skipping 864 matching lines @@
   int since_epoch = static_cast<int>(timer_.Elapsed().InMicroseconds());
   const char* format = (se == START) ? "timer-event-start,\"%s\",%ld"
                                      : "timer-event-end,\"%s\",%ld";
   msg.Append(format, name, since_epoch);
   msg.WriteToLogFile();
 }
 
 
 void Logger::EnterExternal(Isolate* isolate) {
   LOG(isolate, TimerEvent(START, TimerEventExternal::name()));
-  TRACE_EVENT_BEGIN0(TRACE_DISABLED_BY_DEFAULT("v8"), "V8.External");
   DCHECK(isolate->current_vm_state() == JS);
   isolate->set_current_vm_state(EXTERNAL);
 }
 
 
 void Logger::LeaveExternal(Isolate* isolate) {
   LOG(isolate, TimerEvent(END, TimerEventExternal::name()));
-  TRACE_EVENT_END0(TRACE_DISABLED_BY_DEFAULT("v8"), "V8.External");
   DCHECK(isolate->current_vm_state() == EXTERNAL);
   isolate->set_current_vm_state(JS);
 }
 
 
 template <class TimerEvent>
 void TimerEventScope<TimerEvent>::LogTimerEvent(Logger::StartEnd se) {
   Logger::CallEventLogger(isolate_, TimerEvent::name(), se,
                           TimerEvent::expose_to_api());
 }
@@ skipping 931 matching lines @@
     removeCodeEventListener(jit_logger_);
     delete jit_logger_;
     jit_logger_ = NULL;
   }
 
   return log_->Close();
 }
 
 }  // namespace internal
 }  // namespace v8