[Tracing] Use TracingCategoryObserver in gc statistics

src/d8.cc

 // Copyright 2012 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 <errno.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/stat.h>
 
 #include <algorithm>
@@ skipping 2834 matching lines @@
   }
   create_params.array_buffer_allocator = Shell::array_buffer_allocator;
 #ifdef ENABLE_VTUNE_JIT_INTERFACE
   create_params.code_event_handler = vTune::GetVtuneCodeEventHandler();
 #endif
   create_params.constraints.ConfigureDefaults(
       base::SysInfo::AmountOfPhysicalMemory(),
       base::SysInfo::AmountOfVirtualMemory());
 
   Shell::counter_map_ = new CounterMap();
-  if (i::FLAG_dump_counters || i::FLAG_track_gc_object_stats) {
+  if (i::FLAG_dump_counters || i::FLAG_gc_stats) {
     create_params.counter_lookup_callback = LookupCounter;
     create_params.create_histogram_callback = CreateHistogram;
     create_params.add_histogram_sample_callback = AddHistogramSample;
   }
   Isolate* isolate = Isolate::New(create_params);
   {
     Isolate::Scope scope(isolate);
     Initialize(isolate);
     PerIsolateData data(isolate);
 
@@ skipping 96 matching lines @@
 }
 
 }  // namespace v8
 
 
 #ifndef GOOGLE3
 int main(int argc, char* argv[]) {
   return v8::Shell::Main(argc, argv);
 }
 #endif