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 { context: ctx } = this.cachedCanvases.getCanvas(
        "isFontSubpixelAAEnabled",
        10,
        10
      );
      ctx.scale(1.5, 1);
      ctx.fillText("I", 0, 10);
      const data = ctx.getImageData(0, 0, 10, 10).data;
      let enabled = false;
      for (let i = 3; i < data.length; i += 4) {
        if (data[i] > 0 && data[i] < 255) {
          enabled = true;
          break;
        }
      }
      return shadow(this, "isFontSubpixelAAEnabled", enabled);
    }
    showText(glyphs) {
      const current = this.current;
      const font = current.font;
      if (font.isType3Font) {
        return this.showType3Text(glyphs);
      }
      const fontSize = current.fontSize;
      if (fontSize === 0) {