RFR: JDK-8282933: Create a test for JDK-4529616

[Srinivas Mandalika]

AccessibleJTableCell.isShowing() returns false when the cell is actually on
the screen.
The test validates the fix for the above issue by verifying that the isShowing call returns true when invoked via the  accessiblity context.

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Commit messages:
 - 8282933:Create a test for JDK-4529616
 - 8282933:Create a test for JDK-4529616

Changes: https://git.openjdk.java.net/jdk/pull/7783/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7783&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8282933
  Stats: 82 lines in 1 file changed: 82 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7783.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7783/head:pull/7783

PR: https://git.openjdk.java.net/jdk/pull/7783