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 paths = this.pendingTextPaths;
      const ctx = this.ctx;
      if (paths === undefined) {
        ctx.beginPath();
        return;
      }
      ctx.save();
      ctx.beginPath();
      for (let i = 0; i < paths.length; i++) {
        const path = paths[i];
        ctx.setTransform.apply(ctx, path.transform);
        ctx.translate(path.x, path.y);
        path.addToPath(ctx, path.fontSize);
      }
      ctx.restore();
      ctx.clip();
      ctx.beginPath();
      delete this.pendingTextPaths;
    }
    setCharSpacing(spacing) {
      this.current.charSpacing = spacing;
    }
    setWordSpacing(spacing) {
      this.current.wordSpacing = spacing;
    }
    setHScale(scale) {
      this.current.textHScale = scale / 100;
    }
    setLeading(leading) {