Add support for dispatch contexts on BindingSet

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

Index: mojo/public/cpp/bindings/lib/binding_state.h
diff --git a/mojo/public/cpp/bindings/lib/binding_state.h b/mojo/public/cpp/bindings/lib/binding_state.h
index efc7a711675fefbbc1108a481a96d01cacbbb280..4fc35803163467f2306275e89c41e1c70df095d2 100644
--- a/mojo/public/cpp/bindings/lib/binding_state.h
+++ b/mojo/public/cpp/bindings/lib/binding_state.h
@@ -131,6 +131,8 @@ class MultiplexedBindingState {
   MultiplexedBindingState();
   ~MultiplexedBindingState();
 
+  void AddFilter(std::unique_ptr<MessageReceiver> filter);
+
   bool HasAssociatedInterfaces() const;
 
   void PauseIncomingMethodCallProcessing();