CSS understands fractional pixel lengths and Blink does layout in LayoutUnits, but somewhere along the way things get snapped to DIP boundaries even on high density displays.

See http://jsbin.com/vokater/edit and screenshot from a Retina MBP.  If we snapped to physical pixels instead of DIPs, the y-offset of the middle box would be in between the y-offsets of the left and right boxes.

Safari seems to get this right.

(Perhaps issue 485650 will fix this?)
 

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