hg: jdk/client: 8226697: Several tests which need the @key headful keyword are missing it.

[philip.race at oracle.com]

Changeset: e7671524d4e2
Author:    prr
Date:      2019-06-24 17:31 -0700
URL:       http://hg.openjdk.java.net/jdk/client/rev/e7671524d4e2

8226697: Several tests which need the @key headful keyword are missing it.
Reviewed-by: serb

! test/jdk/com/sun/java/swing/plaf/gtk/4928019/bug4928019.java
! test/jdk/com/sun/java/swing/plaf/gtk/Test6635110.java
! test/jdk/com/sun/java/swing/plaf/gtk/Test6963870.java