Setup Required:
DSF = Device Scale Factor
2 Displays, left is at 2x DSF (192dpi) and the right is at 1x DSF (96 dpi).

1) Navigate to a webpage which has comboboxes (HTML select control) on the left and right halves of the renderer view.
2) Drag the Chrome window to the right to associate it with the 1x DSF.
3) Drag the Chrome window to the left enough so that it spans both windows but doesn't associate with the 2x display. At least one combobox should be on both displays each.
4) Click on the combobox on the 1x display. All is well.
5) Click on the combobox on the 2x display. The renderer view shrinks.