<Swing Dev> [9] Fix for JDK-7172750 : Nimbus ScrollBar:ScrollBarThumb[Pressed].backgroundPainter is never invoked

[Ajit Ghaisas]

Hi,

Bug : 
     https://bugs.openjdk.java.net/browse/JDK-7172750

Issue :
    Nimbus ScrollBar:ScrollBarThumb[Pressed].backgroundPainter is never invoked
    
Root Cause :
    There is no differentiation between 'MouseOver' and Mouse 'Pressed' in scroll thumb painting.

Fix :
     1. Used existing member boolean 'dragging' from BasicScrollBarUI class in SynthScrollBarUI class to differentiate between "mouse over" and "mouse pressed" state.
     2. Added a test case - it passes on Windows, Linux and Mac.

Please review the webrev : 
    http://cr.openjdk.java.net/~aghaisas/7172750/webrev.00/

Regards,
Ajit