Add ImmutableHeap class consisting of parts

src/vm/heap.h

 // Copyright (c) 2014, the Fletch project authors. Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
 #ifndef SRC_VM_HEAP_H_
 #define SRC_VM_HEAP_H_
 
 #include "src/shared/globals.h"
 #include "src/shared/random.h"
 #include "src/vm/object.h"
@@ skipping 99 matching lines @@
 
   void AddWeakPointer(HeapObject* object, WeakPointerCallback callback);
   void RemoveWeakPointer(HeapObject* object);
   void ProcessWeakPointers();
   void VisitWeakObjectPointers(PointerVisitor* visitor) {
     WeakPointer::Visit(weak_pointers_, visitor);
   }
 
  private:
   friend class ExitReference;
+  friend class ImmutableHeap;
   Heap(Space* existing_space, WeakPointer* weak_pointers);
 
   Object* CreateStringInternal(Class* the_class, int length, bool clear,
                                bool immutable);
 
   Object* AllocateRawClass(int size);
 
   // Used for initializing identity hash codes for immutable objects.
   RandomLCG* random_;
   Space* space_;
@@ skipping 32 matching lines @@
   return object->IsSmi()
       ? Smi::cast(object)->value()
       : LargeInteger::cast(object)->value();
 }
 
 
 }  // namespace fletch
 
 
 #endif  // SRC_VM_HEAP_H_