First pass at a connection matrix...

[Christine Flood]

This is just experimental for now.  The long term plan is to have this matrix built by write barriers and have a smarter metric for choosing connected collection set regions.  

The matrix is built and printed during concurrent marking if you run with -XX:+ShenandoahMatrix.
The somewhat silly heuristic is run via -XX:ShenandoahGCHeuristics=connections.

This isn't really integrated with the new region_in_collection_set stuff, but is enough for now.

http://cr.openjdk.java.net/~chf/connections/webrev.01/


Christine