Merge

7085906: Replace the permgen allocated sentinelRef with a self-looped end Summary: Remove the sentinelRef and let the last Reference in a discovered chain point back to itself. Reviewed-by: ysr, jmasa

7050392: G1: Introduce flag to generate a log of the G1 ergonomic decisions Summary: It introduces ergonomic decision logging in G1 for the following heuristics: heap sizing, collection set construction, concurrent cycle initiation, and partially-young GC start/end. The code has a bit of refactoring in a few places to make the decision logging possible. It also replaces alternative ad-hoc logging that we have under different parameters and switches (G1_DEBUG, G1PolicyVerbose). Reviewed-by: johnc, ysr