6845368: large objects cause a crash or unexpected exception Reviewed-by: jmasa, iveresov

6861660: OopMapBlock count/size confusion Reviewed-by: tonyp, iveresov

Merge

6871111: G1: remove the concurrent overhead tracker Summary: Removing the concurrent overhead tracker from G1, along with the GC overhead reporter and the G1AccountConcurrentOverhead (both of which rely on the the concurrent overhead tracker). Reviewed-by: iveresov, johnc