RFR: 8236651: Simplify and update glass gtk backend

Fri Jul 3 13:53:23 UTC 2020

On Sun, 14 Jun 2020 23:59:17 GMT, Thiago Milczarek Sayao <tsayao at openjdk.org> wrote:

>> This is the result on OL 82 with latest commit
>> <img width="596" alt="OL82"
>> src="https://user-images.githubusercontent.com/6153953/84592508-d82c5200-ae63-11ea-87d3-7f55671ed302.png">
>
> @pankaj-bansal Sorry for commiting again. Now the Tab Pane test works properly.

> If you want these commits to be preserved when you integrate, you will need to make a 'merge-style' pull request.

Please ignore this information from Skara. I don't know what caused it, but I've pinged the Skara folks about it.

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PR: https://git.openjdk.java.net/jfx/pull/77