<Swing Dev> RFR: 8272229: BasicSplitPaneDivider:oneTouchExpandableChanged() returns letButton and rightButton as null with GTKLookAndFeel.

[Pankaj Bansal]

The function documentation for oneTouchExpandableChanged states that the function does couple of things, but in reality  it only does those things if the Look and Feel supports the supportsOneTouchButtons. In case the Look and Feel does not support supportsOneTouchButtons, this functions just returns in beginning and does not do anything.
This change clarifies the above in function documentation.

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Commit messages:
 - 8272229: BasicSplitPaneDivider:oneTouchExpandableChanged() returns leftButton and rightButton as null with GTKLookAndFeel.

Changes: https://git.openjdk.java.net/jdk/pull/5263/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5263&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8272229
  Stats: 4 lines in 1 file changed: 1 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5263.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5263/head:pull/5263

PR: https://git.openjdk.java.net/jdk/pull/5263