[runtime] Support Proxy setPrototypeOf trap

src/runtime/runtime-proxy.cc

Index: src/runtime/runtime-proxy.cc
diff --git a/src/runtime/runtime-proxy.cc b/src/runtime/runtime-proxy.cc
index 5a12f1050aff985065973386035f552dc1dee377..d1b3238ccbd0b7e1cf1798f590352368c8e2a2c7 100644
--- a/src/runtime/runtime-proxy.cc
+++ b/src/runtime/runtime-proxy.cc
@@ -31,9 +31,8 @@ RUNTIME_FUNCTION(Runtime_CreateJSProxy) {
         isolate, NewTypeError(MessageTemplate::kProxyHandlerNonObject));
   }
   if (handler->IsJSProxy() && !JSProxy::cast(*handler)->has_handler()) {
-    // TODO(cbruni): Use better error message.
-    THROW_NEW_ERROR_RETURN_FAILURE(
-        isolate, NewTypeError(MessageTemplate::kProxyHandlerNonObject));
+    THROW_NEW_ERROR_RETURN_FAILURE(isolate,
+                                   NewTypeError(MessageTemplate::kProtoNotSet));
   }
   instance->set_target(*target);
   instance->set_handler(*handler);