Read isolate from page, not through map.

src/objects-visiting.h

-// Copyright 2006-2009 the V8 project authors. All rights reserved.
+// Copyright 2011 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
 //       with the distribution.
@@ skipping 193 matching lines @@
   }
 };
 
 
 template<typename StaticVisitor, typename BodyDescriptor, typename ReturnType>
 class FlexibleBodyVisitor : public BodyVisitorBase<StaticVisitor> {
  public:
   static inline ReturnType Visit(Map* map, HeapObject* object) {
     int object_size = BodyDescriptor::SizeOf(map, object);
     BodyVisitorBase<StaticVisitor>::IteratePointers(
-        map->heap(),
+        map->GetHeap(),
         object,
         BodyDescriptor::kStartOffset,
         object_size);
     return static_cast<ReturnType>(object_size);
   }
 
   template<int object_size>
   static inline ReturnType VisitSpecialized(Map* map, HeapObject* object) {
     ASSERT(BodyDescriptor::SizeOf(map, object) == object_size);
     BodyVisitorBase<StaticVisitor>::IteratePointers(
-        map->heap(),
+        map->GetHeap(),
         object,
         BodyDescriptor::kStartOffset,
         object_size);
     return static_cast<ReturnType>(object_size);
   }
 };
 
 
 template<typename StaticVisitor, typename BodyDescriptor, typename ReturnType>
 class FixedBodyVisitor : public BodyVisitorBase<StaticVisitor> {
  public:
   static inline ReturnType Visit(Map* map, HeapObject* object) {
     BodyVisitorBase<StaticVisitor>::IteratePointers(
-        map->heap(),
+        map->GetHeap(),
         object,
         BodyDescriptor::kStartOffset,
         BodyDescriptor::kEndOffset);
     return static_cast<ReturnType>(BodyDescriptor::kSize);
   }
 };
 
 
 // Base class for visitors used for a linear new space iteration.
 // IterateBody returns size of visited object.
@@ skipping 160 matching lines @@
 
   for (; !it.done(); it.next()) {
     it.rinfo()->template Visit<StaticVisitor>(heap);
   }
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_VISITING_H_