RFR: 8252935: Add treeShowing listener only when needed [v3]

[John Hendrikx]

On Thu, 28 Jan 2021 13:37:59 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

>> John Hendrikx has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - Add performance test
>>  - Use registerChangeListener in ProgressIndicatorSkin
>
> The updated fix using `registerChangeListener` and the test look good. I left a few mostly-minor comments.

I think this change is complete now, including an integration test and tests on all new code.  Please let me know if anything else needs to be done.

> modules/javafx.graphics/src/main/java/com/sun/javafx/scene/TreeShowingExpression.java line 2:
> 
>> 1: /*
>> 2:  * Copyright (c) 2013, 2020, Oracle and/or its affiliates. All rights reserved.
> 
> change 2020 to 2021

Solved, and also did this in all other files included in this change.

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PR: https://git.openjdk.java.net/jfx/pull/185