Reduce space usage of simple transitions and descriptors holders.

src/objects-visiting-inl.h

 // 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 312 matching lines @@
 
 template<typename StaticVisitor>
 void StaticMarkingVisitor<StaticVisitor>::MarkTransitionArray(
     Heap* heap, TransitionArray* transitions) {
   if (!StaticVisitor::MarkObjectWithoutPush(heap, transitions)) return;
 
   // Skip recording the descriptors_pointer slot since the cell space
   // is not compacted and descriptors are referenced through a cell.
   StaticVisitor::MarkObject(heap, transitions->descriptors_pointer());
 
+  // Simple transitions do not have keys nor prototype transitions.
+  if (transitions->IsSimpleTransition()) return;
+
   if (transitions->HasPrototypeTransitions()) {
     // Mark prototype transitions array but do not push it onto marking
     // stack, this will make references from it weak. We will clean dead
     // prototype transitions in ClearNonLiveTransitions.
     Object** slot = transitions->GetPrototypeTransitionsSlot();
     HeapObject* obj = HeapObject::cast(*slot);
     heap->mark_compact_collector()->RecordSlot(slot, slot, obj);
     StaticVisitor::MarkObjectWithoutPush(heap, obj);
   }
 
@@ skipping 54 matching lines @@
   RelocIterator it(this, mode_mask);
   for (; !it.done(); it.next()) {
     it.rinfo()->template Visit<StaticVisitor>(heap);
   }
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_VISITING_INL_H_