Add workaround for redefinition of __proto__ property.

src/runtime.cc

 // Copyright 2012 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 4073 matching lines @@
 
   // Special case for callback properties.
   if (result.IsPropertyCallbacks()) {
     Object* callback = result.GetCallbackObject();
     // To be compatible with Safari we do not change the value on API objects
     // in Object.defineProperty(). Firefox disagrees here, and actually changes
     // the value.
     if (callback->IsAccessorInfo()) {
       return isolate->heap()->undefined_value();
     }
+    // TODO(mstarzinger): The __proto__ property should actually be a real
+    // JavaScript accessor instead of a foreign callback. But for now we just
+    // avoid changing the writability attribute of this property.
+    Handle<String> proto_string = isolate->factory()->proto_string();
+    if (callback->IsForeign() && proto_string->Equals(*name)) {
+      attr = static_cast<PropertyAttributes>(attr & ~READ_ONLY);

[rossberg, 2013/03/04 16:04:42]

As discussed offline, this should also filter DONT_DELETE. More importantly,
DONT_DELETE should be false initially.

[Michael Starzinger, 2013/03/04 16:24:58]

Done.

+    }
     // Avoid redefining foreign callback as data property, just use the stored
     // setter to update the value instead.
     // TODO(mstarzinger): So far this only works if property attributes don't
     // change, this should be fixed once we cleanup the underlying code.
     if (callback->IsForeign() && result.GetAttributes() == attr) {
       return js_object->SetPropertyWithCallback(callback,
                                                 *name,
                                                 *obj_value,
                                                 result.holder(),
                                                 kStrictMode);
@@ skipping 9206 matching lines @@
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     isolate->counters()->gc_last_resort_from_js()->Increment();
     isolate->heap()->CollectAllGarbage(Heap::kNoGCFlags,
                                        "Runtime::PerformGC");
   }
 }
 
 
 } }  // namespace v8::internal