[jfx25u] RFR: 8367306: HeaderButtonOverlayTest fails to compile with TEST_SDK_PATH

[Ambarish Rapte]

This is a test only fix. 
When using `-PTEST_SDK_PATH=<path>` and `-PTEST_ONLY=true`, the test `HeaderButtonOverlayTest` fails to compile with error: package com.sun.glass.events is not visible.
It would be good to backport this fix so that test passes with `-PTEST_SDK_PATH=<path>`

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Commit messages:
 - Backport 3e376e66a3510f8dee7abb52344961caee1d114a

Changes: https://git.openjdk.org/jfx25u/pull/34/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx25u&pr=34&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8367306
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jfx25u/pull/34.diff
  Fetch: git fetch https://git.openjdk.org/jfx25u.git pull/34/head:pull/34

PR: https://git.openjdk.org/jfx25u/pull/34