[jdk11u-dev] RFR: 8277396: [TESTBUG] In DefaultButtonModelCrashTest.java, frame is accessed from main thread

[Goetz Lindenmaier]

I backport this for parity with 11.0.16-oracle.

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Commit messages:
 - Backport b310f301efd5390408fb56b62cc09eb9a1604413

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/1059/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=1059&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8277396
  Stats: 23 lines in 1 file changed: 9 ins; 8 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/1059.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/1059/head:pull/1059

PR: https://git.openjdk.java.net/jdk11u-dev/pull/1059