Trace amount of external memory with --trace-gc-verbose.

src/heap.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 389 matching lines @@
                ", committed: %6" V8_PTR_PREFIX "d KB\n",
            lo_space_->SizeOfObjects() / KB,
            lo_space_->Available() / KB,
            lo_space_->CommittedMemory() / KB);
   PrintPID("All spaces,         used: %6" V8_PTR_PREFIX "d KB"
                ", available: %6" V8_PTR_PREFIX "d KB"
                ", committed: %6" V8_PTR_PREFIX "d KB\n",
            this->SizeOfObjects() / KB,
            this->Available() / KB,
            this->CommittedMemory() / KB);
+  PrintPID("External memory reported: %6" V8_PTR_PREFIX "d KB\n",
+           amount_of_external_allocated_memory_ / KB);
   PrintPID("Total time spent in GC  : %.1f ms\n", total_gc_time_ms_);
 }
 
 
 // TODO(1238405): Combine the infrastructure for --heap-stats and
 // --log-gc to avoid the complicated preprocessor and flag testing.
 void Heap::ReportStatisticsAfterGC() {
   // Similar to the before GC, we use some complicated logic to ensure that
   // NewSpace statistics are logged exactly once when --log-gc is turned on.
 #if defined(DEBUG)
@@ skipping 7648 matching lines @@
   if (FLAG_parallel_recompilation) {
     heap_->relocation_mutex_->Lock();
 #ifdef DEBUG
     heap_->relocation_mutex_locked_by_optimizer_thread_ =
         heap_->isolate()->optimizing_compiler_thread()->IsOptimizerThread();
 #endif  // DEBUG
   }
 }
 
 } }  // namespace v8::internal