[ic] Simplify handling of primitive maps.

src/string-stream.cc

Index: src/string-stream.cc
diff --git a/src/string-stream.cc b/src/string-stream.cc
index 3ae4580709c25ab058983c6d00b873e18ba82991..acfb9174141ba19ef8d1bc8ca342619b95b30e07 100644
--- a/src/string-stream.cc
+++ b/src/string-stream.cc
@@ -533,7 +533,7 @@ void StringStream::PrintPrototype(JSFunction* fun, Object* receiver) {
     print_name = true;
   } else if (isolate->context() != nullptr) {
     if (!receiver->IsJSObject()) {
-      receiver = receiver->GetRootMap(isolate)->prototype();
+      receiver = receiver->GetPrototypeChainRootMap(isolate)->prototype();
     }
 
     for (PrototypeIterator iter(isolate, JSObject::cast(receiver),