<Swing Dev> RFR: 8196090: javax/swing/JComboBox/6559152/bug6559152.java fails

[Prasanta Sadhukhan]

Please review a test fix for a test issue seen where correct item of combobox is not selected.
The issue seems to stem from the fact the key events was processed without waiting for the frame to show up and also
delay between key events was less as it used ExtendedRobot which by default sets delay between events to 20ms so key
event was not processed correctly in mach5 system. Added robot delay to allow frame to show up and also replaced
ExtendedRobot to awt Robot and sets delay to 100ms to be consistent as it is used for other tests. Mach5 job was run
for several iteration on all 3 platforms. Link in JBS

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Commit messages:
 - 8196090: javax/swing/JComboBox/6559152/bug6559152.java fails

Changes: https://git.openjdk.java.net/jdk/pull/700/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=700&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8196090
  Stats: 14 lines in 2 files changed: 7 ins; 3 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/700.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/700/head:pull/700

PR: https://git.openjdk.java.net/jdk/pull/700