RFR: 8223392: Add missing BitMap comments for JDK-8222986

[Thomas Schatzl]

Hi,

On Mon, 2019-05-06 at 13:14 +0200, Stefan Karlsson wrote:
> Hi all,
> 
> Please review this small patch to add comments that should have been 
> pushed with JDK-8222986.
> 
> http://cr.openjdk.java.net/~stefank/8223392/webrev.01/
> https://bugs.openjdk.java.net/browse/JDK-8223392
> 

  looks good and trivial.

Thomas