message: don't report pong_timeout errors to bindings
diff: @@ -413,6 +413,7 @@ void SyncSession::handle_error(SyncError error)
  // Connection level errors
  case ProtocolError::connection_closed:
  case ProtocolError::other_error:
  + case ProtocolError::pong_timeout:
  // Not real errors, don't need to be reported to the binding.
  return;
  case ProtocolError::unknown_message:
  @@ -423,7 +424,6 @@ void SyncSession::handle_error(SyncError error)
  case ProtocolError::reuse_of_session_ident:
  case ProtocolError::bound_in_other_session:
  case ProtocolError::bad_message_order:
  - case ProtocolError::pong_timeout:
  break;
  // Session errors
  case ProtocolError::session_closed:
  