Make ServiceRegistry (which implements) ApplicationConnection just wrap a ServiceProviderImpl.

mojo/public/cpp/application/service_provider_impl.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MOJO_PUBLIC_APPLICATION_SERVICE_PROVIDER_IMPL_H_
 #define MOJO_PUBLIC_APPLICATION_SERVICE_PROVIDER_IMPL_H_
 
 #include <functional>
 #include <string>
 #include <utility>
@@ skipping 17 matching lines @@
   // drop |interface_request| (as implied  by the interface).
   template <typename Interface>
   using InterfaceRequestHandler =
       std::function<void(const ConnectionContext& connection_context,
                          InterfaceRequest<Interface> interface_request)>;
 
   // Constructs this service provider implementation in an unbound state.
   ServiceProviderImpl();
 
   // Constructs this service provider implementation, binding it to the given
-  // interface request.
+  // interface request. Note: If |service_provider_request| is not valid
+  // ("pending"), then the object will be put into an unbound state.
   explicit ServiceProviderImpl(
       const ConnectionContext& connection_context,
       InterfaceRequest<ServiceProvider> service_provider_request);
 
   ~ServiceProviderImpl() override;
 
   // Binds this service provider implementation to the given interface request.
   // This may only be called if this object is unbound.
   void Bind(const ConnectionContext& connection_context,
             InterfaceRequest<ServiceProvider> service_provider_request);
@@ skipping 96 matching lines @@
 
   internal::ServiceConnectorRegistry service_connector_registry_;
   ServiceProvider* fallback_service_provider_;
 
   MOJO_DISALLOW_COPY_AND_ASSIGN(ServiceProviderImpl);
 };
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_APPLICATION_SERVICE_PROVIDER_IMPL_H_