RFR: 8346324: javax/swing/JScrollBar/4865918/bug4865918.java fails in CI

[Prasanta Sadhukhan]

javax/swing/JScrollBar/4865918/bug4865918.java fails in CI citing

java.lang.RuntimeException: The scrollbar block increment is incorrect
at bug4865918.main(bug4865918.java:60) 

Seems like scrollbar is not in focus when mouse is pressed..Used CountDownLatch to mage focus gain more determinisitic.
Fix is passing in CI in several CI systems

-------------

Commit messages:
 - test fix

Changes: https://git.openjdk.org/jdk/pull/22783/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22783&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8346324
  Stats: 10 lines in 1 file changed: 10 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/22783.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22783/head:pull/22783

PR: https://git.openjdk.org/jdk/pull/22783