<Swing Dev> [9] JDK-8165213: [TESTBUG] [PIT] consistent failure of a new regtest for 8163193

[Shashidhara Veerabhadraiah]

Hi All,
	Please review fix for JDK-8165213 where there is a consistent failure while testing for gradient color of the button.

Issue: The Robot's function to get the pixel's RGB values has an issue with its implementation and is currently getting resolved. Because of this issue, we are getting incorrect RGB values for the requested pixel and hence the test is getting failed.

Resolution\Fix: There is an alternate mechanism to capture the image to a buffer and use the buffer function to get the RGB values. This test is for HiDpi displays. In the image space, the images won't be scaled implicitly and hence they need to be applied with the scaling in the graphics space before painting on to the image buffer. This same is implemented.
Based on the test outputs, the tolerance band for color comparison is set at 11.

Test outputs: 
1. On a windows system, the pixel color values exactly matches.
2. On a Linux system, the pixel color values vary by a maximum difference of around 6.
3. On a mac system, the pixel color values vary by a maximum difference of around 10.

Bug: https://bugs.openjdk.java.net/browse/JDK-8165213
Webrev: http://cr.openjdk.java.net/~pkbalakr/shashi/8165213/webrev_01/

Thanks and regards,
Shashi