[runtime] Support proxies as return value of API constructors.

src/builtins/builtins-api.cc

Index: src/builtins/builtins-api.cc
diff --git a/src/builtins/builtins-api.cc b/src/builtins/builtins-api.cc
index 5ad518b8428c6637b99c5d05b4ec5a14d49d701f..52023efd65cfe55139b3223ed55f7149d7ccdf62 100644
--- a/src/builtins/builtins-api.cc
+++ b/src/builtins/builtins-api.cc
@@ -118,7 +118,8 @@ MUST_USE_RESULT MaybeHandle<Object> HandleApiCallHelper(
     }
     // Rebox the result.
     result->VerifyApiCallResultType();
-    if (!is_construct || result->IsJSObject()) return handle(*result, isolate);
+    if (!is_construct || result->IsJSReceiver())
+      return handle(*result, isolate);
   }
 
   return js_receiver;