Always print external time in --trace-gc to make it toolable.

src/heap/gc-tracer.cc

 // Copyright 2014 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/v8.h"
 
 #include "src/heap/gc-tracer.h"
 
 namespace v8 {
 namespace internal {
@@ skipping 342 matching lines @@
   }
   Output("%8.0f ms: ", heap_->isolate()->time_millis_since_init());
 
   Output("%s %.1f (%.1f) -> %.1f (%.1f) MB, ", current_.TypeName(false),
          static_cast<double>(current_.start_object_size) / MB,
          static_cast<double>(current_.start_memory_size) / MB,
          static_cast<double>(current_.end_object_size) / MB,
          static_cast<double>(current_.end_memory_size) / MB);
 
   int external_time = static_cast<int>(current_.scopes[Scope::EXTERNAL]);
-  if (external_time > 0) Output("%d / ", external_time);
+  double duration = current_.end_time - current_.start_time;
+  Output("%.1f / %d ms", duration, external_time);
 
-  double duration = current_.end_time - current_.start_time;
-  Output("%.1f ms", duration);
   if (current_.type == Event::SCAVENGER) {
     if (current_.incremental_marking_steps > 0) {
       Output(" (+ %.1f ms in %d steps since last GC)",
              current_.incremental_marking_duration,
              current_.incremental_marking_steps);
     }
   } else {
     if (current_.incremental_marking_steps > 0) {
       Output(
           " (+ %.1f ms in %d steps since start of marking, "
@@ skipping 345 matching lines @@
 
 
 bool GCTracer::SurvivalEventsRecorded() const {
   return survival_events_.size() > 0;
 }
 
 
 void GCTracer::ResetSurvivalEvents() { survival_events_.reset(); }
 }  // namespace internal
 }  // namespace v8