internal/api_classic.go
func ClassicContextFromContext(ctx netcontext.Context) (appengine.Context, error) {
	c := fromContext(ctx)
	if c == nil {
		return nil, errNotAppEngineContext
	}
	return c, nil
}
func ClassicContextFromContext(ctx netcontext.Context) (appengine.Context, error) {
	c := fromContext(ctx)
	if c == nil {
		return nil, errNotAppEngineContext
	}
	return c, nil
}
// This is only for classic App Engine adapters.