RFR (XS): 8213829: Remove circular dependency between g1CollectedHeap and g1ConcurrentMark

[Kim Barrett]

> On Nov 14, 2018, at 1:29 AM, Man Cao <manc at google.com> wrote:
> 
> Hi all,
> 
> Could anyone review this small cleanup patch that noticeably reduces size of build output (and likely build time)?
> 
> Webrev: https://cr.openjdk.java.net/~manc/8213829/webrev.00/
> RFE: https://bugs.openjdk.java.net/browse/JDK-8213829
> 
> Thanks,
> Man

Change looks good.

But I don’t understand the underlying problem.  I would have guessed the include guards would prevent
things that would lead to increased build size or build times (and possibly prevent compilation due to
forward references, but that’s clearly not been happening).