RFR: 8214699: Node.getPseudoClassStates must return the same instance on every call

[Jeanette Winzenburg]

On Thu, 18 Jun 2020 16:30:42 GMT, Ambarish Rapte <arapte at openjdk.org> wrote:

> Node.getPseudoClassStates() returns a new UnmodifiableObservableSet of PseudoClassState on each call. So in order to
> listen to any changes in this set, user must call the method Node.getPseudoClassStates() only once and keep a strong
> reference to the returned UnmodifiableObservableSet.
>  
> So the fix is that the method Node.getPseudoClassStates() should return the same UnmodifiableObservableSet on every
> call. As the returned set is an UnmodifiableObservableSet, it will not have any impact on it's usage.
>  
> Added a small unit test. and,
> Altered(minor) a test which was modified in
> past(https://github.com/openjdk/jfx/commit/0ac98695a1b11443c342fad4f009d6e03a052522)
> (https://github.com/openjdk/jfx/commit/62323e0a9c5817b33daa262d6914eba0e8d274ff) along with this method and should be
> updated in view of this change.

forgot to comment the test (can't seem to be able to add to a review?)

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Changes requested by fastegal (Committer).

PR: https://git.openjdk.java.net/jfx/pull/253