<Swing Dev> RFR: 8198400: Test javax/swing/SwingUtilities/6797139/bug6797139.java fails in mach5

[Prasanta Sadhukhan]

Please review a test fix for an issue seen failing in mach5 testing although it is not reproducible locally.
The issue seems to stem from the fact that the test was been run as headless test although it requires to create UI
class like ComponentUI which is needed for painting, layout calculations etc and therefore it fails citing

_no ComponentUI class for:
javax.swing.JButton[,0,0,0x0,invalid,alignmentX=0.0,alignmentY=0.0,border=,flags=0,maximumSize=,minimumSize=,preferredSize=,defaultIcon=,disabledIcon=,disabledSelectedIcon=,margin=null,paintBorder=true,paintFocus=true,pressedIcon=,rolloverEnabled=false,rolloverIcon=,rolloverSelectedIcon=,selectedIcon=,text=Probably,defaultCapable=true]_

Modified the test to mark it as headful.
Mach5 job was run for several iteration on all 3 platforms. Link in JBS

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Commit messages:
 - 8198400: Test javax/swing/SwingUtilities/6797139/bug6797139.java fails in mach5

Changes: https://git.openjdk.java.net/jdk/pull/719/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=719&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8198400
  Stats: 3 lines in 2 files changed: 0 ins; 2 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/719.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/719/head:pull/719

PR: https://git.openjdk.java.net/jdk/pull/719