Build a GraphQLSchema for use by client tools.

Given the result of a client running the introspection query, creates and returns a GraphQLSchema instance which can be then used with all graphql-js tools, but cannot be used to execute a query, as introspection does not represent the "resolver", "parse" or "serialize" functions or any other server-internal mechanisms.

This function expects a complete introspection result. Don't forget to check the "errors" field of a server response before calling this function.