RFR: 8287912: GTK L&F : Background of tree icons are red [v4]

[Prasanta Sadhukhan]

On Tue, 6 Sep 2022 07:07:53 GMT, Abhishek Kumar <duke at openjdk.org> wrote:

>> The background of tree icons are not red in GTK LAF when setOpaque is set to false for tree component.
>> It has been observed that while painting tree cell background in GTK LAF, a rectangular area is also painted with background color (white). 
>> 
>> Proposed solution is to check the opacity of tree component before drawing tree cell background. If the opacity is set to "false" then the background shouldn't be painted.
>> 
>> An automated test case has been added and checked in CI, link is added in JBS.
>
> Abhishek Kumar has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Empty 1st line removed in test

Marked as reviewed by psadhukhan (Reviewer).

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PR: https://git.openjdk.org/jdk/pull/10112