<Swing Dev> RFR: 8193942: Regression automated test '/open/test/jdk/javax/swing/JFrame/8175301/ScaledFrameBackgroundTest.java' fails

[Prasanta Sadhukhan]

This test use to fail in macos in mach5 nightly testing long time back. It used to fail in ubuntu17.10 due to unsupported wayland display mode. Recent run of this test on supported platforms does not fail.
Modified the test slightly to be consistent with other test regarding robot delays, moved frame to center of screen.
Mach5 job running several iterations of the test in all platforms is ok. Link in JBS.

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Commit messages:
 - 8193942: Regression automated test '/open/test/jdk/javax/swing/JFrame/8175301/ScaledFrameBackgroundTest.java' fails

Changes: https://git.openjdk.java.net/jdk/pull/1923/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1923&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8193942
  Stats: 5 lines in 2 files changed: 1 ins; 1 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1923.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1923/head:pull/1923

PR: https://git.openjdk.java.net/jdk/pull/1923