Don't allow seal or element property definition on external arrays.

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 3396 matching lines @@
     return isolate->heap()->false_value();
   }
 
   if (IsJSGlobalProxy()) {
     Object* proto = GetPrototype();
     if (proto->IsNull()) return this;
     ASSERT(proto->IsJSGlobalObject());
     return JSObject::cast(proto)->PreventExtensions();
   }
 
+  // It's not possible to seal objects with external array elements
+  if (HasExternalArrayElements()) {
+    HandleScope scope(isolate);
+    Handle<Object> object(this);
+    Handle<Object> error  =
+        isolate->factory()->NewTypeError(
+            "cant_prevent_ext_external_array_elements",
+            HandleVector(&object, 1));
+    return isolate->Throw(*error);
+  }
+
   // If there are fast elements we normalize.
   NumberDictionary* dictionary = NULL;
   { MaybeObject* maybe = NormalizeElements();
     if (!maybe->To<NumberDictionary>(&dictionary)) return maybe;
   }
   ASSERT(HasDictionaryElements() || HasDictionaryArgumentsElements());
   // Make sure that we never go back to fast case.
   dictionary->set_requires_slow_elements();
 
   // Do a map transition, other objects with this map may still
@@ 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