<AWT Dev> RFR: 8253977: More memory leaks in client-libs on macOS

[Sergey Bylokhov]

While working on the JDK-8240709 I have found that the test created for JDK-8134947 (currently executed on macOS only)
can fail due to memory leaks(more often if change it to be stricter). See my comments inline.

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Commit messages:
 - Initial fix

Changes: https://git.openjdk.java.net/jdk/pull/514/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=514&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253977
  Stats: 183 lines in 5 files changed: 134 ins; 11 del; 38 mod
  Patch: https://git.openjdk.java.net/jdk/pull/514.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/514/head:pull/514

PR: https://git.openjdk.java.net/jdk/pull/514