Put making embedded maps in optimized code weak behind a flag.

src/mark-compact.cc

 // 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 67 matching lines @@
     for (Object** current = start; current < end; current++) {
       if ((*current)->IsHeapObject()) {
         HeapObject* object = HeapObject::cast(*current);
         CHECK(HEAP->mark_compact_collector()->IsMarked(object));
       }
     }
   }
 
   void VisitEmbeddedPointer(RelocInfo* rinfo) {
     ASSERT(rinfo->rmode() == RelocInfo::EMBEDDED_OBJECT);
-    if (rinfo->host()->kind() != Code::OPTIMIZED_FUNCTION ||
+    if (!FLAG_weak_embedded_maps_in_optimized_code ||
+        rinfo->host()->kind() != Code::OPTIMIZED_FUNCTION ||
         !rinfo->target_object()->IsMap() ||
         !Map::cast(rinfo->target_object())->CanTransition()) {
       VisitPointer(rinfo->target_object_address());
     }
   }
 };
 
 
 static void VerifyMarking(Address bottom, Address top) {
   VerifyMarkingVisitor visitor;
@@ skipping 3811 matching lines @@
   while (buffer != NULL) {
     SlotsBuffer* next_buffer = buffer->next();
     DeallocateBuffer(buffer);
     buffer = next_buffer;
   }
   *buffer_address = NULL;
 }
 
 
 } }  // namespace v8::internal