Added automated test for 8262518:SwingNode.setContent does not close previous content, resulting in memory leak
------------- Commit messages: - jckeck fix - 8315317: Add test for JDK-8262518 Changes: https://git.openjdk.org/jfx/pull/1228/files Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1228&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8315317 Stats: 137 lines in 1 file changed: 137 ins; 0 del; 0 mod Patch: https://git.openjdk.org/jfx/pull/1228.diff Fetch: git fetch https://git.openjdk.org/jfx.git pull/1228/head:pull/1228 PR: https://git.openjdk.org/jfx/pull/1228
