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

[Kevin Rushforth]

On Sun, 24 Jan 2021 15:25:06 GMT, John Hendrikx <jhendrikx at openjdk.org> wrote:

>> This is a PoC for performance testing.  
>> 
>> It contains commented out code in PopupWindow and ProgressIndicatorSkin and two tests are failing because of that.
>> 
>> This code avoids registering two listeners (on Scene and on Window) for each and every Node to support the aforementioned classes.  The complete change should update these two classes to add their own listeners instead.
>
> 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.

tests/system/src/test/java/test/javafx/scene/NodeTreeShowingTest.java line 2:

> 1: /*
> 2:  * Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.

2021

tests/system/src/test/java/test/javafx/scene/NodeTreeShowingTest.java line 125:

> 123:         });
> 124: 
> 125:         for(int j = 0; j < 5; j++) {

MInor: add space after `for`

tests/system/src/test/java/test/javafx/scene/NodeTreeShowingTest.java line 49:

> 47: /**
> 48:  * TODO fix
> 49:  * This test is based on the test case reported in JDK-8209830

Comment block needs to be updated to describe this bug.

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

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

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