Mark maps having a hidden prototype rather than maps of hidden prototypes.

src/string-stream.cc

Index: src/string-stream.cc
diff --git a/src/string-stream.cc b/src/string-stream.cc
index 2801d23cda088b784916aaf3ccdf5c30e7efcab6..43be8f1f1872e3a3581a5a81b51f70fb83ddc155 100644
--- a/src/string-stream.cc
+++ b/src/string-stream.cc
@@ -527,12 +527,18 @@ void StringStream::PrintPrototype(JSFunction* fun, Object* receiver) {
   Object* name = fun->shared()->name();
   bool print_name = false;
   Isolate* isolate = fun->GetIsolate();
-  for (PrototypeIterator iter(isolate, receiver,
-                              PrototypeIterator::START_AT_RECEIVER);
-       !iter.IsAtEnd(); iter.Advance()) {
-    if (iter.GetCurrent()->IsJSObject()) {
+  if (receiver->IsNull() || receiver->IsUndefined() || receiver->IsJSProxy()) {
+    print_name = true;
+  } else {
+    if (!receiver->IsJSObject()) {
+      receiver = receiver->GetRootMap(isolate)->prototype();
+    }
+
+    for (PrototypeIterator iter(isolate, JSObject::cast(receiver),
+                                PrototypeIterator::START_AT_RECEIVER);
+         !iter.IsAtEnd(); iter.Advance()) {
       Object* key = iter.GetCurrent<JSObject>()->SlowReverseLookup(fun);
-      if (key != isolate->heap()->undefined_value()) {
+      if (!key->IsUndefined()) {
         if (!name->IsString() ||
             !key->IsString() ||
             !String::cast(name)->Equals(String::cast(key))) {
@@ -542,9 +548,8 @@ void StringStream::PrintPrototype(JSFunction* fun, Object* receiver) {
           print_name = false;
         }
         name = key;
+        break;
       }
-    } else {
-      print_name = true;
     }
   }
   PrintName(name);