[mojo] Add GenericInterface_ to interface class variants

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 82b1a327b21a13d318f9bf82d3de6e4c473472d0..dea3a6b906724d09d20666dc4e5822a5b00e0580 100644
--- a/mojo/public/cpp/bindings/lib/binding_state.h
+++ b/mojo/public/cpp/bindings/lib/binding_state.h
@@ -37,6 +37,8 @@ class BindingState;
 template <typename Interface>
 class BindingState<Interface, false> {
  public:
+  using GenericInterface = typename Interface::GenericInterface;
+
   explicit BindingState(Interface* impl) : impl_(impl) {
     stub_.set_sink(impl_);
   }
@@ -81,9 +83,9 @@ class BindingState<Interface, false> {
     DestroyRouter();
   }
 
-  InterfaceRequest<Interface> Unbind() {
-    InterfaceRequest<Interface> request =
-        MakeRequest<Interface>(router_->PassMessagePipe());
+  InterfaceRequest<GenericInterface> Unbind() {
+    InterfaceRequest<GenericInterface> request =
+        MakeRequest<GenericInterface>(router_->PassMessagePipe());
     DestroyRouter();
     return request.Pass();
   }
@@ -128,6 +130,8 @@ class BindingState<Interface, false> {
 template <typename Interface>
 class BindingState<Interface, true> {
  public:
+  using GenericInterface = typename Interface::GenericInterface;
+
   explicit BindingState(Interface* impl) : impl_(impl) {
     stub_.set_sink(impl_);
   }
@@ -177,10 +181,10 @@ class BindingState<Interface, true> {
     router_ = nullptr;
   }
 
-  InterfaceRequest<Interface> Unbind() {
+  InterfaceRequest<GenericInterface> Unbind() {
     endpoint_client_.reset();
-    InterfaceRequest<Interface> request =
-        MakeRequest<Interface>(router_->PassMessagePipe());
+    InterfaceRequest<GenericInterface> request =
+        MakeRequest<GenericInterface>(router_->PassMessagePipe());
     router_ = nullptr;
     return request.Pass();
   }