<Swing Dev> RFR: 8253980: javax/swing/plaf/synth/7158712/bug7158712.java fails on windows

[Prasanta Sadhukhan]

This test was seen to be failing in mach5 hidpi system on windows.
The test actually checks for the fact that popup size should be 10 pixels wider than the comboBox width and the popup
should overlap the comboBox by 5 pixels (negative y-offset) which maynot exactly be same in hidpi mode. Fix is to make
it run for scale 1 as the fix is not dependant on hidpi mode. Also, some cleanup is done like changing setAutoDelay()
which is normally set to 100ms for several other tests to make it consistent. Also, mach5 run for several iterations is
green and link is posted in JBS.

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Commit messages:
 - 8253980: javax/swing/plaf/synth/7158712/bug7158712.java fails on windows

Changes: https://git.openjdk.java.net/jdk/pull/500/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=500&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253980
  Stats: 14 lines in 2 files changed: 7 ins; 1 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/500.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/500/head:pull/500

PR: https://git.openjdk.java.net/jdk/pull/500