RFR: 8202813: Move vm_weak processing from SystemDictionary::do_unloading to WeakProcessor

[Kim Barrett]

> On May 17, 2018, at 9:17 PM, Kim Barrett <kim.barrett at oracle.com> wrote:
> 
>> On May 17, 2018, at 3:13 AM, Stefan Johansson <stefan.johansson at oracle.com> wrote:
>> I agree that baby steps is often good, but now when JFR is in would it make sense to include more in this change?
> 
> OK, I can do that.
> 
>> 
>> I would like it to be added when needed, to make sure we only include the parts we really need. Right now it would be hard for me to review those parts since I can't verify that they work as intended. I'm mostly concerned about the parts around serial/parallel phases, which is currently unused.
> 
> Since you and (privately) Coleen are both complaining about this, I’ll reconsider.
> 
> Withdrawing this change for now.

I've merged with jfr changes and updated per StefanJ's comments.
In particular, SystemDictionary::oops_do is gone.  This involved
changing JFR's leak profiler to call always_strong_oops_do instead,
which is what I think it should have been calling all along.

However, SystemDictionary::roots_oops_do still conditionally processes
SystemDictionary::vm_weak_oop_storage().  Coleen thinks that shouldn't
be needed, but I'm not ready to get rid of it yet, and would like to
defer that to a later change.

No incremental webrev.  It was kind of messy with the JFR merge
conflict and the parameter change, so didn't seem worthwhile trying to
generate.

New webrev:
http://cr.openjdk.java.net/~kbarrett/8202813/open.01/