Mojo C++ bindings: add more perf tests for Router/MultiplexRouter.

mojo/public/cpp/bindings/lib/interface_endpoint_client.cc

Index: mojo/public/cpp/bindings/lib/interface_endpoint_client.cc
diff --git a/mojo/public/cpp/bindings/lib/interface_endpoint_client.cc b/mojo/public/cpp/bindings/lib/interface_endpoint_client.cc
index 368a521612be364cd18f71bc0f54b4aaea278252..6140cde5399374583bfef8d7cb53c0408e680d1c 100644
--- a/mojo/public/cpp/bindings/lib/interface_endpoint_client.cc
+++ b/mojo/public/cpp/bindings/lib/interface_endpoint_client.cc
@@ -152,7 +152,8 @@ InterfaceEndpointClient::InterfaceEndpointClient(
 
   // TODO(yzshen): the way to use validator (or message filter in general)
   // directly is a little awkward.
-  filters_.Append(std::move(payload_validator));
+  if (payload_validator)
+    filters_.Append(std::move(payload_validator));
 
   controller_ = handle_.group_controller()->AttachEndpointClient(
       handle_, this, task_runner_);