Fix a prototype chain traversal not expecting proxies.

src/objects.cc

 // 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 3977 matching lines @@
     if (result->IsProperty()) return;
   }
   result->NotFound();
 }
 
 
 // Search object and it's prototype chain for callback properties.
 void JSObject::LookupCallback(String* name, LookupResult* result) {
   Heap* heap = GetHeap();
   for (Object* current = this;
-       current != heap->null_value();
+       current != heap->null_value() && current->IsJSObject();
        current = JSObject::cast(current)->GetPrototype()) {
     JSObject::cast(current)->LocalLookupRealNamedProperty(name, result);
     if (result->IsProperty() && result->type() == CALLBACKS) return;
   }
   result->NotFound();
 }
 
 
 // Search for a getter or setter in an elements dictionary.  Returns either
 // undefined if the element is read-only, or the getter/setter pair (fixed
@@ skipping 8171 matching lines @@
   if (break_point_objects()->IsUndefined()) return 0;
   // Single break point.
   if (!break_point_objects()->IsFixedArray()) return 1;
   // Multiple break points.
   return FixedArray::cast(break_point_objects())->length();
 }
 #endif
 
 
 } }  // namespace v8::internal