manually inlining validator functions improves performance

Lets take the isAbsolute function of posix in the path module.

  /**
   * @param {string} path
   * @returns {boolean}
   */
  isAbsolute(path) {
    validateString(path, 'path');
    return path.length > 0 &&
           StringPrototypeCharCodeAt(path, 0) === CHAR_FORWARD_SLASH;
  },

Benchmark it:

./node benchmark/path/isAbsolute-posix.js 
path/isAbsolute-posix.js n=100000 path="": 26,199,553.088023424
path/isAbsolute-posix.js n=100000 path=".": 19,512,560.625525866
path/isAbsolute-posix.js n=100000 path="/foo/bar": 15,003,530.33068681
path/isAbsolute-posix.js n=100000 path="/baz/..": 20,841,496.252698973
path/isAbsolute-posix.js n=100000 path="bar/baz": 25,044,717.342815597

inline validateString

  /**
   * @param {string} path
   * @returns {boolean}
   */
  isAbsolute(path) {
    if (typeof path !== 'string')
      throw new ERR_INVALID_ARG_TYPE('path', 'string', path);
    return path.length > 0 &&
           StringPrototypeCharCodeAt(path, 0) === CHAR_FORWARD_SLASH;
  },

./node benchmark/path/isAbsolute-posix.js 
path/isAbsolute-posix.js n=100000 path="": 49,143,043.605605446
path/isAbsolute-posix.js n=100000 path=".": 36,665,695.025748484
path/isAbsolute-posix.js n=100000 path="/foo/bar": 20,950,367.322790273
path/isAbsolute-posix.js n=100000 path="/baz/..": 22,806,405.772027623
path/isAbsolute-posix.js n=100000 path="bar/baz": 41,722,470.470921524

Annoying...

Start with benchmark/path/isAbsolute-posix.js and reproduce the two benchmark runs for the posix path isAbsolute case. Compare the results and inspect the corresponding path-module implementation to determine whether validator inlining is intended beyond this example; the issue does not name a target source file, tests, or completion criteria.