Add flag to trace object groups

src/heap/heap.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 "src/heap/heap.h"
 
 #include "src/accessors.h"
 #include "src/api.h"
 #include "src/ast/scopeinfo.h"
 #include "src/base/bits.h"
@@ skipping 1383 matching lines @@
       if (!gc_prologue_callbacks_[i].pass_isolate) {
         v8::GCCallback callback = reinterpret_cast<v8::GCCallback>(
             gc_prologue_callbacks_[i].callback);
         callback(gc_type, flags);
       } else {
         v8::Isolate* isolate = reinterpret_cast<v8::Isolate*>(this->isolate());
         gc_prologue_callbacks_[i].callback(isolate, gc_type, flags);
       }
     }
   }
+  if (FLAG_trace_object_groups && (gc_type == kGCTypeIncrementalMarking ||
+                                   gc_type == kGCTypeMarkSweepCompact)) {
+    isolate_->global_handles()->PrintObjectGroups();
+  }
 }
 
 
 void Heap::CallGCEpilogueCallbacks(GCType gc_type,
                                    GCCallbackFlags gc_callback_flags) {
   for (int i = 0; i < gc_epilogue_callbacks_.length(); ++i) {
     if (gc_type & gc_epilogue_callbacks_[i].gc_type) {
       if (!gc_epilogue_callbacks_[i].pass_isolate) {
         v8::GCCallback callback = reinterpret_cast<v8::GCCallback>(
             gc_epilogue_callbacks_[i].callback);
@@ skipping 4929 matching lines @@
 }
 
 
 // static
 int Heap::GetStaticVisitorIdForMap(Map* map) {
   return StaticVisitorBase::GetVisitorId(map);
 }
 
 }  // namespace internal
 }  // namespace v8