Check global object behind global proxy for extensibility

src/accessors.cc

Index: src/accessors.cc
diff --git a/src/accessors.cc b/src/accessors.cc
index 1e8abd95ab6adc13d11d904826847e533fe8a559..0366895bfc332dc9949c25b22eaa982612b3b1b7 100644
--- a/src/accessors.cc
+++ b/src/accessors.cc
@@ -136,6 +136,12 @@ bool SetPropertyOnInstanceIfInherited(
     // This behaves sloppy since we lost the actual strict-mode.
     // TODO(verwaest): Fix by making ExecutableAccessorInfo behave like data
     // properties.
+    if (object->IsJSGlobalProxy()) {
+      PrototypeIterator iter(isolate, object);
+      if (iter.IsAtEnd()) return true;
+      DCHECK(PrototypeIterator::GetCurrent(iter)->IsJSGlobalObject());
+      object = Handle<JSObject>::cast(PrototypeIterator::GetCurrent(iter));
+    }
     if (!object->map()->is_extensible()) return true;
     JSObject::SetOwnPropertyIgnoreAttributes(object, Utils::OpenHandle(*name),
                                              value, NONE).Check();