Bugfix: make dependent code field in AllocationSite weak.

src/objects.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 8174 matching lines @@
       ElementsKind boilerplate_elements_kind);
   static inline AllocationSiteMode GetMode(ElementsKind from, ElementsKind to);
   static inline bool CanTrack(InstanceType type);
 
   static const int kTransitionInfoOffset = HeapObject::kHeaderSize;
   static const int kNestedSiteOffset = kTransitionInfoOffset + kPointerSize;
   static const int kDependentCodeOffset = kNestedSiteOffset + kPointerSize;
   static const int kWeakNextOffset = kDependentCodeOffset + kPointerSize;
   static const int kSize = kWeakNextOffset + kPointerSize;
 
+  // During mark compact we need to take special care for the dependent code
+  // field.
+  static const int kPointerFieldsBeginOffset = kTransitionInfoOffset;
+  static const int kPointerFieldsEndOffset = kDependentCodeOffset;
+
+  // For other visitors, use the fixed body descriptor below.
   typedef FixedBodyDescriptor<HeapObject::kHeaderSize,
                               kDependentCodeOffset + kPointerSize,
                               kSize> BodyDescriptor;
 
  private:
   inline DependentCode::DependencyGroup ToDependencyGroup(Reason reason);
   DISALLOW_IMPLICIT_CONSTRUCTORS(AllocationSite);
 };
 
 
@@ skipping 2362 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_