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)

gl.uniform2f(cache.resolutionLocation, width, height);
    
    let count = 0;
    for (let i = 0, ii = figures.length; i < ii; i++) {
      switch (figures[i].type) {
        case "lattice":
          const rows =
            (figures[i].coords.length / figures[i].verticesPerRow) | 0;
          count += (rows - 1) * (figures[i].verticesPerRow - 1) * 6;
          break;
        case "triangles":
          count += figures[i].coords.length;
          break;
      }
    }
    
    const coords = new Float32Array(count * 2);
    const colors = new Uint8Array(count * 3);
    const coordsMap = context.coords,
      colorsMap = context.colors;
    let pIndex = 0,
      cIndex = 0;
    for (let i = 0, ii = figures.length; i < ii; i++) {
      const figure = figures[i],
        ps = figure.coords,
        cs = figure.colors;
      switch (figure.type) {
        case "lattice":
          const cols = figure.verticesPerRow;
          const rows = (ps.length / cols) | 0;