Mojo C++ bindings: support disconnect with a reason.

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

Index: mojo/public/cpp/bindings/lib/control_message_handler.cc
diff --git a/mojo/public/cpp/bindings/lib/control_message_handler.cc b/mojo/public/cpp/bindings/lib/control_message_handler.cc
index b112489475bd29e525495a1fec9af93c54d6c8a9..bfd785df087a2135482251916840f9d7716d52e4 100644
--- a/mojo/public/cpp/bindings/lib/control_message_handler.cc
+++ b/mojo/public/cpp/bindings/lib/control_message_handler.cc
@@ -141,6 +141,13 @@ bool ControlMessageHandler::RunOrClosePipe(Message* message) {
   auto& input = *params_ptr->input;
   if (input.is_require_version())
     return interface_version_ >= input.get_require_version()->version;
+  else if (input.is_send_disconnect_reason()) {
+    disconnect_custom_reason_ =
+        input.get_send_disconnect_reason()->custom_reason;
+    disconnect_description_ =
+        std::move(input.get_send_disconnect_reason()->description);
+    return true;
+  }
 
   return false;
 }