get MIN_TOUCH_DISTANCE_TO_PINCH() {
    // The 35 is coming from:
    //  https://searchfox.org/mozilla-central/source/gfx/layers/apz/src/GestureEventListener.cpp#36
    //
    // The properties TouchEvent::screenX/Y are in screen CSS pixels:
    //  https://developer.mozilla.org/en-US/docs/Web/API/Touch/screenX#examples
    // MIN_TOUCH_DISTANCE_TO_PINCH is in CSS pixels.
    return 35 / OutputScale.pixelRatio;
  }
NOTE: Don't shadow this value since `devicePixelRatio` may change if the
window resolution changes, e.g. if the viewer is moved to another monitor.