Add safe interface for collections of UniquePersistent

src/global-handles.h

 // 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
@@ skipping 143 matching lines @@
   // Returns the current number of weak handles to global objects.
   // These handles are also included in NumberOfWeakHandles().
   int NumberOfGlobalObjectWeakHandles();
 
   // Returns the current number of handles to global objects.
   int global_handles_count() const {
     return number_of_global_handles_;
   }
 
   // Clear the weakness of a global handle.
-  static void ClearWeakness(Object** location);
+  static void* ClearWeakness(Object** location);
 
   // Clear the weakness of a global handle.
   static void MarkIndependent(Object** location);
 
   // Mark the reference to this object externaly unreachable.
   static void MarkPartiallyDependent(Object** location);
 
   static bool IsIndependent(Object** location);
 
   // Tells whether global handle is near death.
@@ skipping 225 matching lines @@
   List<int> new_space_indices_;
   int singleton_handles_[NUMBER_OF_SINGLETON_HANDLES];
 
   DISALLOW_COPY_AND_ASSIGN(EternalHandles);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_GLOBAL_HANDLES_H_