Remove V8.External traces due to its high overhead

The Tracing split CL https://codereview.chromium.org/1707563002 mostly moved the location of
the TRACE call, but it added 2 very high frequency calls related to tracking V8.External.

In most benchmark and devices the added overhead is negligible except on N6 where it gets amplified.
This CL removes those 2 calls until more efficient tracing or a different technique is used.

BUG=588137
LOG=N

Review URL: https://codereview.chromium.org/1765673003

Cr-Commit-Position: refs/heads/master@{#34499}

src/log.cc

@@ -882,7 +882,6 @@ void Logger::TimerEvent(Logger::StartEnd se, const char* name) {
 
 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);
 }
@@ -890,7 +889,6 @@ void Logger::EnterExternal(Isolate* isolate) {
 
 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);
 }

src/vm-state-inl.h

@@ -40,11 +40,8 @@ inline const char* StateToString(StateTag state) {
 template <StateTag Tag>
 VMState<Tag>::VMState(Isolate* isolate)
     : isolate_(isolate), previous_tag_(isolate->current_vm_state()) {
-  if (previous_tag_ != EXTERNAL && Tag == EXTERNAL) {
-    if (FLAG_log_timer_events) {
-      LOG(isolate_, TimerEvent(Logger::START, TimerEventExternal::name()));
-    }
-    TRACE_EVENT_BEGIN0(TRACE_DISABLED_BY_DEFAULT("v8"), "V8.External");
+  if (FLAG_log_timer_events && previous_tag_ != EXTERNAL && Tag == EXTERNAL) {
+    LOG(isolate_, TimerEvent(Logger::START, TimerEventExternal::name()));
   }
   isolate_->set_current_vm_state(Tag);
 }
@@ -52,11 +49,8 @@ VMState<Tag>::VMState(Isolate* isolate)
 
 template <StateTag Tag>
 VMState<Tag>::~VMState() {
-  if (previous_tag_ != EXTERNAL && Tag == EXTERNAL) {
-    if (FLAG_log_timer_events) {
-      LOG(isolate_, TimerEvent(Logger::END, TimerEventExternal::name()));
-    }
-    TRACE_EVENT_END0(TRACE_DISABLED_BY_DEFAULT("v8"), "V8.External");
+  if (FLAG_log_timer_events && previous_tag_ != EXTERNAL && Tag == EXTERNAL) {
+    LOG(isolate_, TimerEvent(Logger::END, TimerEventExternal::name()));
   }
   isolate_->set_current_vm_state(previous_tag_);
 }