Add support for dispatch contexts on BindingSet

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

Index: mojo/public/cpp/bindings/lib/binding_state.cc
diff --git a/mojo/public/cpp/bindings/lib/binding_state.cc b/mojo/public/cpp/bindings/lib/binding_state.cc
index 2d892a071b1f5125ec473300d5ed44361348ef68..6beae550a2378c897f99a580cbdba759e34aa4bd 100644
--- a/mojo/public/cpp/bindings/lib/binding_state.cc
+++ b/mojo/public/cpp/bindings/lib/binding_state.cc
@@ -79,6 +79,12 @@ MultiplexedBindingState::MultiplexedBindingState() = default;
 
 MultiplexedBindingState::~MultiplexedBindingState() = default;
 
+void MultiplexedBindingState::AddFilter(
+    std::unique_ptr<MessageReceiver> filter) {
+  DCHECK(endpoint_client_);
+  endpoint_client_->AddFilter(std::move(filter));
+}
+
 bool MultiplexedBindingState::HasAssociatedInterfaces() const {
   return router_ ? router_->HasAssociatedEndpoints() : false;
 }