RFR: 8283507: Create a regression test for RFE 4287690 [v3]

[Manukumar V S]

> Create a regression test for [JDK-4287690](https://bugs.openjdk.java.net/browse/JDK-4287690)
> Issue description:
> I want JComboBox to send an event just before the popup (drop down) list is displayed.
> 
> Fix:
> This requires some additional API targeted for major release of the JDK (1.4).The PopupMenuEvent will from the JPopupMenu will be forwarded to the JComboBox. A client of the JComboBox can register itself as a PopupMenuListener to receive the notification.
> So JComboBox should send drop down events when the drop down popup is visible as well as invisible. JComboBox.addPopupMenuListener(PopupMenuListener) can be used to register for pop up events.
> 
> Testing:
> Tested using Mach5 in all platforms available(macos,linux and windows) and got all pass.

Manukumar V S has updated the pull request incrementally with one additional commit since the last revision:

  Review comment fixed: Removed unwanted directory

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7906/files
  - new: https://git.openjdk.java.net/jdk/pull/7906/files/38a5e19e..cba696d7

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7906&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7906&range=01-02

  Stats: 0 lines in 1 file changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7906.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7906/head:pull/7906

PR: https://git.openjdk.java.net/jdk/pull/7906