resolve(relativePath) {
    const selfDirPath = path.dirname(this._filePath);
    const resolvedPath = path.resolve(selfDirPath, relativePath);
    const resolvedRelativePath = path.relative(path.dirname(this._inDirPath), resolvedPath);
    return this._slash(resolvedRelativePath);
  }
resolve file path on this file.
@param {string} relativePath - relative path on this file.