JSplitPane's divider (BasicSplitPaneDivider) is inconvenient for painting because extends Container but not JComponent. For example, there is no a simple way to change divider color or background color. Also you cannot control divider opacity.

Probably the right thing is to inherit BasicSplitPaneDivider from JComponent instead of Container.

This CR is tightly coupled with the 6580370 CR.