[heap] Record references in the new code objects in heap::CopyCode.

src/heap/scavenger-inl.h

 // Copyright 2015 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.
 
 #ifndef V8_HEAP_SCAVENGER_INL_H_
 #define V8_HEAP_SCAVENGER_INL_H_
 
 #include "src/heap/scavenger.h"
 
 namespace v8 {
@@ skipping 37 matching lines @@
     ScavengeObject(reinterpret_cast<HeapObject**>(slot), heap_object);
 
     object = *slot;
     // If the object was in from space before and is after executing the
     // callback in to space, the object is still live.
     // Unfortunately, we do not know about the slot. It could be in a
     // just freed free space object.
     if (heap->InToSpace(object)) {
       return KEEP_SLOT;
     }
-  } else {
-    DCHECK(!heap->InNewSpace(object));
   }
+  // Slots can point to "to" space if the slot has been recorded multiple
+  // times in the remembered set. We remove the redundant slot now.
   return REMOVE_SLOT;
 }
 
 // static
 template <PromotionMode promotion_mode>
 void StaticScavengeVisitor<promotion_mode>::VisitPointer(Heap* heap,
                                                          HeapObject* obj,
                                                          Object** p) {
   Object* object = *p;
   if (!heap->InNewSpace(object)) return;
   Scavenger::ScavengeObject(reinterpret_cast<HeapObject**>(p),
                             reinterpret_cast<HeapObject*>(object));
 }
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_SCAVENGER_INL_H_