<Swing Dev> RFR: 8171381: [TEST_BUG] [macos] javax/swing/JPopupMenu/7156657/bug7156657.java fails on OS X

[Alexander Zuev]

Replaces usage of SunToolkit.realSync() with Robot.waitForIdle()

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Commit messages:
 - 8171381: [TEST_BUG] [macos] javax/swing/JPopupMenu/7156657/bug7156657.java fails on OS X

Changes: https://git.openjdk.java.net/jdk/pull/3606/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3606&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8171381
  Stats: 8 lines in 1 file changed: 0 ins; 4 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3606.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3606/head:pull/3606

PR: https://git.openjdk.java.net/jdk/pull/3606