RFR: 8282937: Write a regression test for JDK-4820080

[Manukumar V S]

Write a regression test for [JDK-4820080](https://bugs.openjdk.java.net/browse/JDK-4820080) : RFE: Cannot Change the JSplitPane Divider Color while dragging

Issue(as per bug description):
I want to change the color of the JSplitPane divider. I
opened the code and found that, the color is hard coded to
darkGray while one is dragging the splitDivider. I have an
application where the components on SplitPane have black
background, So when i drag I can not see the split getting
dragged. Can some one fix this, by externelising the
SplitDivider color so that it can be changed at run time.

Testing:
Java 1.4.1 -> Test Failed.
$ ./j2sdk1.4.1/bin/java JSplitPaneDragColorTest
Metal uses correct drag color false
CDE/Motif uses correct drag color false
Windows uses correct drag color false
Test Failed.

Java 1.5.0 -> Test Failed.
$ ./jdk1.5.0/bin/java JSplitPaneDragColorTest
Metal uses correct drag color true
Windows uses correct drag color true
Windows Classic uses correct drag color true
Test Passed.

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Commit messages:
 - 8282937: Write a regression test for JDK-4820080

Changes: https://git.openjdk.java.net/jdk/pull/7803/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7803&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8282937
  Stats: 194 lines in 1 file changed: 194 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7803.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7803/head:pull/7803

PR: https://git.openjdk.java.net/jdk/pull/7803