Use dimensions cached in resizeInfo for resize calculations

The logic requires the size of $resizable when the resizing started.
This is already stored in this.resizeInfo, but for some reason the
code recalculates every time, which is both inefficient and wrong
(but not a problem at the moment as $resizable doesn't change size
until resizeEnd).

Change-Id: I37a3c98e24b9e7d5e1970212975cef5ce9ef8a99
Merge "Use dimensions cached in resizeInfo for resize calculations"