RFR: 8287876: The recently de-problemlisted TestTitledBorderLeak test is unstable [v2]

[Sergey Bylokhov]

> This is an update of the test which was de-problemlisted [here](https://github.com/openjdk/jdk/pull/8450).
> 
> Looks like the initial root cause of the issue was related to the last disposed frame which for some reason was not deleted from the memory, for that issue, the [next](https://bugs.openjdk.org/browse/JDK-8287707) bug was reported.
> But that change also replaced the usage of weak references by the Runtime.getRuntime().freeMemory() which is not stable enough to verify the leak - its return values vary a lot.
> 
> This change returns the usage of weak references and tests only one instance of TitledBorder which is enough to verify the old [bug](https://bugs.openjdk.org/browse/JDK-8204963).

Sergey Bylokhov has updated the pull request incrementally with one additional commit since the last revision:

  Smaller version

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/9051/files
  - new: https://git.openjdk.java.net/jdk/pull/9051/files/da1a82c9..125bf43d

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=9051&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=9051&range=00-01

  Stats: 14 lines in 1 file changed: 0 ins; 14 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/9051.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/9051/head:pull/9051

PR: https://git.openjdk.java.net/jdk/pull/9051