Fix debug name inferring wrt proxies

src/string-stream.cc

Index: src/string-stream.cc
diff --git a/src/string-stream.cc b/src/string-stream.cc
index 43be8f1f1872e3a3581a5a81b51f70fb83ddc155..02f6f1c2bb81d4b6b710b4f16568b143488c0015 100644
--- a/src/string-stream.cc
+++ b/src/string-stream.cc
@@ -537,6 +537,7 @@ void StringStream::PrintPrototype(JSFunction* fun, Object* receiver) {
     for (PrototypeIterator iter(isolate, JSObject::cast(receiver),
                                 PrototypeIterator::START_AT_RECEIVER);
          !iter.IsAtEnd(); iter.Advance()) {
+      if (iter.GetCurrent()->IsJSProxy()) break;
       Object* key = iter.GetCurrent<JSObject>()->SlowReverseLookup(fun);
       if (!key->IsUndefined()) {
         if (!name->IsString() ||