RFR(M): 8248401: Refactor/unify RMI gc support functionality

[Thomas Schatzl]

Hi all,

   can I have reviews for this change that unifies RMI gc support across 
collectors.

Based on an idea that came up by Kim in recent reviews, instead of every 
collector implementing that support by itself, the change moves the 
details into CollectedHeap and the collectors only need to call an 
appropriate method.

That method has formerly called CollectedHeap::millis_since_last_gc() 
which has a confusing name. I chose "last_whole_heap_examined_time" 
instead which I believe is while long, more appropriate. I did not find 
a good shorter name, I am open for issues.

For testing I used implemented originally for JDK-8248401 (at 
http://cr.openjdk.java.net/~tschatzl/8248401/webrev.test/). It still is 
very much dependent on not having a too big delay between a GC and the 
call to the RMI method. I do not know how to make it more stable either, 
and fearing false positives I did not add it to this CR. I could be 
convinced to do so if you think we should take the risk or have a better 
idea on how it could be improved.

CR:
https://bugs.openjdk.java.net/browse/JDK-8248401
Webrev:
http://cr.openjdk.java.net/~tschatzl/8248401/webrev
Testing:
tier1-5; plus mentioned test

Thanks,
   Thomas