Make object groups and implicit references a bit more lightweight.

src/profile-generator.cc

 // Copyright 2010 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 2277 matching lines @@
 void NativeObjectsExplorer::FillRetainedObjects() {
   if (embedder_queried_) return;
   Isolate* isolate = Isolate::Current();
   // Record objects that are joined into ObjectGroups.
   isolate->heap()->CallGlobalGCPrologueCallback();
   List<ObjectGroup*>* groups = isolate->global_handles()->object_groups();
   for (int i = 0; i < groups->length(); ++i) {
     ObjectGroup* group = groups->at(i);
     if (group->info_ == NULL) continue;
     List<HeapObject*>* list = GetListMaybeDisposeInfo(group->info_);
-    for (int j = 0; j < group->objects_.length(); ++j) {
+    for (size_t j = 0; j < group->length_; ++j) {
       HeapObject* obj = HeapObject::cast(*group->objects_[j]);
       list->Add(obj);
       in_groups_.Insert(obj);
     }
     group->info_ = NULL;  // Acquire info object ownership.
   }
   isolate->global_handles()->RemoveObjectGroups();
   isolate->heap()->CallGlobalGCEpilogueCallback();
   // Record objects that are not in ObjectGroups, but have class ID.
   GlobalHandlesExtractor extractor(this);
@@ skipping 777 matching lines @@
 
 
 String* GetConstructorNameForHeapProfile(JSObject* object) {
   if (object->IsJSFunction()) return HEAP->closure_symbol();
   return object->constructor_name();
 }
 
 } }  // namespace v8::internal
 
 #endif  // ENABLE_LOGGING_AND_PROFILING