I was wondering if WebGL is considered stable enough to be enabled by default. It makes some PDFs render much faster and it has been off by default for a while now, so we have had quite some time to test it.

If we decide to enable WebGL by default, we should not forget to update https://github.com/mozilla/pdf.js/blob/master/extensions/chromium/preferences_schema.json#L39 as well.

/cc @yurydelendik 
/cc @Snuffleupagus (because IIRC you were testing WebGL too)

const ps = figure.coords;
    const cs = figure.colors;
    let i, ii;
    switch (figure.type) {
      case "lattice":
        const verticesPerRow = figure.verticesPerRow;
        const rows = Math.floor(ps.length / verticesPerRow) - 1;
        const cols = verticesPerRow - 1;
        for (i = 0; i < rows; i++) {
          let q = i * verticesPerRow;
          for (let j = 0; j < cols; j++, q++) {
            drawTriangle(
              data,
              context,
              ps[q],
              ps[q + 1],
              ps[q + verticesPerRow],
              cs[q],
              cs[q + 1],
              cs[q + verticesPerRow]
            );
            drawTriangle(
              data,
              context,