code: function loadFontNative (fontFace, callback) {
    var theFontFace;
  
    // See if we've previously loaded it.
    if (_loadedFonts[fontFace.id]) {
      return callback(null);
    }
  
    // See if we've previously failed to load it.
    if (_failedFonts[fontFace.id]) {
      return callback(_failedFonts[fontFace.id]);
    }
  
    // System font: assume it's installed.
    if (!fontFace.url) {
      return callback(null);
    }
  
    // Font load is already in progress:
    if (_pendingFonts[fontFace.id]) {
      _pendingFonts[fontFace.id].callbacks.push(callback);
      return;
    }
  
    _pendingFonts[fontFace.id] = {
      startTime: Date.now(),
      callbacks: [callback]
    };
  
    // Use font loader API
    theFontFace = new window.FontFace(fontFace.family,
      'url(' + fontFace.url + ')', fontFace.attributes);
  
    theFontFace.load().then(function () {
      _loadedFonts[fontFace.id] = true;
      callback(null);
    }, function (err) {
      _failedFonts[fontFace.id] = err;
      callback(err);
    });
  }
docs: Internal ======== 
  Native FontFace loader implementation
  @internal