RFR: 8285094: Test java/awt/Frame/InvisibleOwner/InvisibleOwner.java failing on Linux

[Phil Race]

As discussed in https://bugs.openjdk.java.net/browse/JDK-8285094 it seems that the test
java/awt/Frame/GetGraphicsStressTest/GetGraphicsStressTest.java destabilises the Xserver.
This causes java/awt/Frame/InvisibleOwner/InvisibleOwner.java to fail and even before that
other tests which do  pass are not visibly behaving as expected.

I didn't find any Xserver logs of "bad stuff" happening so it just seems like the Xserver was
having trouble keeping up and JDK was behaving correctly as it could despite the Xserver sending
lots of requests to repaint.

Just the "sleep" at the end of GetGraphicsStressTest.java seems to be enough but I'd already
reworked InvisibleOwner.java and I'd like to think it is a bit better than before.

-------------

Commit messages:
 - 8285094
 - 8285094

Changes: https://git.openjdk.java.net/jdk/pull/8312/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8312&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8285094
  Stats: 138 lines in 2 files changed: 74 ins; 9 del; 55 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8312.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8312/head:pull/8312

PR: https://git.openjdk.java.net/jdk/pull/8312