Scroll drift in Chrome when zoomed in

A fun one! Thanks to [this Chromium bug](https://bugs.chromium.org/p/chromium/issues/detail?id=440691), in combination with [these `parseInt`s](https://github.com/emberjs/ember-collection/blob/master/addon/components/ember-collection.js#L102), you can end up in a situation where `ember-collection` slowly scrolls upwards with no user input.

To reproduce, take a look at [the scroll position demo](http://emberjs.com/ember-collection/#/scroll-position) in Chrome, zoom in to 110%, and scroll down a bit.

If you land on anything other than a nice round number, you'll end up in a feedback loop between the `parseInt` truncation in the addon code and the rounding glitch in the browser that inexorably drags you back to the top of the collection.