PDF viewer: recognize pinch-to-zoom on touch screens

On my Chromebook with a touchscreen, pinch-zooming on PDFs in Chrome doesn’t work (thanks to this issue). I was hoping that the Paperpile viewer would correctly capture multi-touch gestures but it doesn’t: it zooms the entire viewport and introduces pixelation, just like the native viewer.

I notice that what’s being rendered is an HTML page of some kind, and there are tons of JavaScript libraries that make recognizing these gestures easy. It would be a big, big help if Paperpile could correctly support this, and I suspect touch screen devices are only going to get more common (various Chromebooks, the Surface Pro, iPad Pro, possibly the next MacBook Pro).