function printCompilerMsg(msg, file) {
  console.error('%s:%d:%d %s - %s',
                file || msg.file, msg.lineno + 1,
                msg.charno + 1, msg.type, msg.error);
  console.error('%s\n%s^',
                msg.line, Array(msg.charno + 1).join(' '));
}
Prints a formatted error or warning message.
@param {CompilerMsg} msg An error or warning message as returned by the
    Closure Compiler Service's JSON output format.
@param {string|null} file The filename to refer to in error messages. If
    null, then msg.file is used instead.