RFR (M): 8034079: G1: Refactor the HeapRegionSet hierarchy

[Bengt Rutisson]

Hi everyone,

Could I have a couple of reviews for this change?

http://cr.openjdk.java.net/~brutisso/8034079/webrev.00/

It tries to simplify the structure of the HeapRegionSets. I need this to 
be able to introduce new types of heap region collections.

Some other cleanups are done as a consequence of this. But there are 
probably still more cleanups to do. I hope that this is a step in the 
right direction.

Here's a short list of some of the changes:

- Class hierarchy simplified
No longer specific subclasses for all instances. Verification code has 
been collected in the super classes and the MT safety checks are 
aggregated instead.

- Proxy sets replaced by HeapRegionSetCount
The use of "proxy sets" was removed in favor of a light weight class to 
keep track of length and capacity.

- G1CollectedHeap::free_region_if_empty() was inlined

- G1CollectedHeap::update_sets_after_freeing_regions() was split up into 
three (or actually four) methods.

- Removed the HRSPhaseSetter, which may soften the verification a bit 
but not much.

- The verification code also prints less information in some cases. But 
instead it prints the relevant information. There is still more cleanup 
that can be done to the messages from the asserts and verifications.

- Moved usage accounting up to avoid having to pass it around as much.

- HeapRegionSetBase::total_used_bytes() was only used in asserts. Did 
not seem worth keeping around.

After these changes the file heapRegionSets.hpp (notice the s at the end 
of the name) was empty so I removed it. However, the heapRegionSets.cpp 
file is still present. I would like to move all the code there in to 
heapRegionSet.cpp, but that would make the webrev more difficult to 
follow. I'm still open to doing that if someone would like me to do it.

Thanks,
Bengt