[Tracing] Use TracingCategoryObserver in gc statistics

src/bootstrapper.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/bootstrapper.h"
 
 #include "src/accessors.h"
 #include "src/api-natives.h"
 #include "src/base/ieee754.h"
 #include "src/code-stubs.h"
@@ skipping 4008 matching lines @@
                                 v8::ExtensionConfiguration* extensions) {
   Isolate* isolate = native_context->GetIsolate();
   ExtensionStates extension_states;  // All extensions have state UNVISITED.
   return InstallAutoExtensions(isolate, &extension_states) &&
          (!FLAG_expose_free_buffer ||
           InstallExtension(isolate, "v8/free-buffer", &extension_states)) &&
          (!FLAG_expose_gc ||
           InstallExtension(isolate, "v8/gc", &extension_states)) &&
          (!FLAG_expose_externalize_string ||
           InstallExtension(isolate, "v8/externalize", &extension_states)) &&
-         (!FLAG_track_gc_object_stats ||
+         (!FLAG_gc_stats ||
           InstallExtension(isolate, "v8/statistics", &extension_states)) &&
          (!FLAG_expose_trigger_failure ||
           InstallExtension(isolate, "v8/trigger-failure", &extension_states)) &&
          (!FLAG_trace_ignition_dispatches ||
           InstallExtension(isolate, "v8/ignition-statistics",
                            &extension_states)) &&
          InstallRequestedExtensions(isolate, extensions, &extension_states);
 }
 
 
@@ skipping 503 matching lines @@
 }
 
 
 // Called when the top-level V8 mutex is destroyed.
 void Bootstrapper::FreeThreadResources() {
   DCHECK(!IsActive());
 }
 
 }  // namespace internal
 }  // namespace v8