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)

this.ctx.transform(a, b, c, d, e, f);
      this._cachedGetSinglePixelWidth = null;
    }
    
    constructPath(ops, args) {
      const ctx = this.ctx;
      const current = this.current;
      let x = current.x,
        y = current.y;
      for (let i = 0, j = 0, ii = ops.length; i < ii; i++) {
        switch (ops[i] | 0) {
          case OPS.rectangle:
            x = args[j++];
            y = args[j++];
            const width = args[j++];
            const height = args[j++];
            const xw = x + width;
            const yh = y + height;