Viewer:  https://mozilla.github.io/pdf.js/web/viewer.html
Chrome on Windows 10
When the attached PDF file is viewed, some of the fonts display as garbled text. 
[Arial, Courier, Times New Roman]
The file views correctly in Adobe Reader.
[fff.pdf](https://github.com/mozilla/pdf.js/files/4652174/fff.pdf)

let charCodes = null;
      for (const charCode in charCodeToGlyphId) {
        if (glyphId === charCodeToGlyphId[charCode]) {
          if (!charCodes) {
            charCodes = [];
          }
          charCodes.push(charCode | 0);
        }
      }
      return charCodes;
    }
    function createCharCode(charCodeToGlyphId, glyphId) {
      for (const charCode in charCodeToGlyphId) {
        if (glyphId === charCodeToGlyphId[charCode]) {
          return charCode | 0;
        }
      }
      newMapping.charCodeToGlyphId[newMapping.nextAvailableFontCharCode] =
        glyphId;
      return newMapping.nextAvailableFontCharCode++;
    }
    const seacs = font.seacs;
    if (newMapping && SEAC_ANALYSIS_ENABLED && seacs && seacs.length) {
      const matrix = properties.fontMatrix || FONT_IDENTITY_MATRIX;
      const charset = font.getCharset();
      const seacMap = Object.create(null);
      for (let glyphId in seacs) {
        glyphId |= 0;
        const seac = seacs[glyphId];
        const baseGlyphName = StandardEncoding[seac[2]];