<Swing Dev> RFR: 8163367: Test javax/swing/JComboBox/8033069/bug8033069NoScrollBar.java javax/swing/JComboBox/8033069/bug8033069ScrollBar.java fails intermittently

[Pankaj Bansal]

The tests a javax/swing/JComboBox/8033069/bug8033069ScrollBar.java and javax/swing/JComboBox/8033069/bug8033069NoScrollBar.java fails intermittently. The tests have a few problems which could cause this behaviour and the are being fixed here.

1. Test access the Swing components without EDT thread at couple of places.
2. Test is not calling waitForIdle or delay after Robot.mouseMove operations.

There is some additional cleanup done in the fix and moved the frame in centre. The tests pass with multiple iterations on CI. Link in the JBS.

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Commit messages:
 - Move frame to centre
 - 8163367: Test javax/swing/JComboBox/8033069/bug8033069NoScrollBar.java javax/swing/JComboBox/8033069/bug8033069ScrollBar.java fails intermittently

Changes: https://git.openjdk.java.net/jdk/pull/3678/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3678&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8163367
  Stats: 32 lines in 2 files changed: 16 ins; 7 del; 9 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3678.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3678/head:pull/3678

PR: https://git.openjdk.java.net/jdk/pull/3678