RFR: 8315825: Open some swing tests [v4]

[Alisen Chung]

> Opening some swing tests:
> 1 javax/swing/LayoutComparator/4907772/bug4907772.java
> 2 javax/swing/LayoutComparator/4979794/bug4979794.java
> 3 javax/swing/LegacyGlueFocusTraversalPolicy/4765272/bug4765272.java
> 4 javax/swing/RootPaneChecking/RootPaneChecking.java

Alisen Chung has updated the pull request incrementally with one additional commit since the last revision:

  fixed btn null error

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/15830/files
  - new: https://git.openjdk.org/jdk/pull/15830/files/5ec823c3..2e7a894e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15830&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15830&range=02-03

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/15830.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15830/head:pull/15830

PR: https://git.openjdk.org/jdk/pull/15830