RFR: 8225777: java/awt/Mixing/MixingOnDialog.java fails on Ubuntu [v2]

[Alexander Zvegintsev]

> Looks like the test started failing after increasing of window's title height in Ubuntu theme:
> 
> ![image](https://user-images.githubusercontent.com/77687766/138088503-f380bcb2-1ffc-4d58-b6b2-2efc56b7975c.png)
> So the click happens on windows title instead of the button.
> 
> For example, macOS has smaller window title height, which allows test to pass.
> <img src="https://user-images.githubusercontent.com/77687766/138088659-bd636518-c23c-4c5e-bf97-61035753c71a.png" width="50%" height="50%">
> 
> Fix moves buttons away from window title.
> ![image](https://user-images.githubusercontent.com/77687766/138088880-a9d1ec38-cde2-437e-80b9-5b7bdf73fd6b.png)
> 
> Testing is green.

Alexander Zvegintsev has updated the pull request incrementally with two additional commits since the last revision:

 - d.setLocationRelativeTo(null);
 - increase auto delay

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6040/files
  - new: https://git.openjdk.java.net/jdk/pull/6040/files/73f085be..f1806ef2

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6040&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6040&range=00-01

  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6040.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6040/head:pull/6040

PR: https://git.openjdk.java.net/jdk/pull/6040