RFR: 8236259: MemoryLeak in ProgressIndicator

[Florian Kirmaier]

Hi everyone,

ticket: https://bugs.openjdk.java.net/browse/JDK-8236259

The fix itself is quite straight forward.
It basically just removed the listener which causes the leak.

The unit-test for the fix is a bit more complicated.

I added a library JMemoryBuddy https://github.com/Sandec/JMemoryBuddy (written by myself), which simplifies testing for memory leaks.
I think there are many places in the JavaFX-codebase that could highly benefit from this library.
It could also simplify many of the already existing unit tests.
It makes testing for memory-leaks readably and reliable. 
It would also be possible to just copy the code of the library into the JavaFX-codebase. 
It only contains a single class.

I also had to make a method public, to write the test. I'm open to ideas, how I could solve it differently.

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Commits:
 - c4da2e7b: JDK-8236259: MemoryLeak in ProgressIndicator - DeterminateIndicator doesn't get collected

Changes: https://git.openjdk.java.net/jfx/pull/71/files
 Webrev: https://webrevs.openjdk.java.net/jfx/71/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8236259
  Stats: 45 lines in 4 files changed: 41 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jfx/pull/71.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/71/head:pull/71

PR: https://git.openjdk.java.net/jfx/pull/71