Missing margin-bottom on large lists with responsive layouts.

[bwh-rl]

Description

In an responsive layout with % item width and fixed item aspect ratios heights will have subpixel. The _rowHeight is measured with offsetHeight, which does not consider subpixel. This leads to an wrong _estScrollHeight, and the missing of the margin-bottom.

Expected outcome

Actual outcome

Live Demo

https://jsbin.com/zifijenavu/edit?html,output

Steps to reproduce

Scroll to the bottom

Browsers Affected

Chrome not tested, but should affect all browsers.

[blasten]

yes, it could use item.getBoundingClientRect().height in https://github.com/PolymerElements/iron-list/blob/master/iron-list.html#L1241 similar to L1239.

[keanulee]

May not be a clear fix - may have perf implications