[FIX] ListBox / DropdownBox: scrollTop issue (zoom != 100% in Chrome)

Chrome returns a floating value when reading the scrollTop value in some
cases (with different zoom levels).
Added rounding when setting "scrollTop" property (as it is of type int)

BCP: 1482025218
Change-Id: Ie8844affbade5124a87afc85d045670f61a75007
Merge "[FIX] ListBox / DropdownBox: scrollTop issue (zoom != 100% in Chrome)"