hg: openjfx/13-dev/rt: 8209938: Default and Cancel button cause memory leak

[ambarish.rapte at oracle.com]

Changeset: ab32008d11a2
Author:    arapte
Date:      2019-07-16 01:20 +0530
URL:       https://hg.openjdk.java.net/openjfx/13-dev/rt/rev/ab32008d11a2

8209938: Default and Cancel button cause memory leak
Reviewed-by: kcr, jvos, nlisker

! modules/javafx.controls/src/main/java/javafx/scene/control/skin/ButtonSkin.java
! modules/javafx.controls/src/test/java/test/javafx/scene/control/ButtonTest.java