RFR (S) 8031818: Experimental VM flag for enforcing safe object construction

[Aleksey Shipilev]

Hi,

Please review the experimental patch for switching the research VM mode
which unconditionally emits the memory barrier at the end of constructor:
  http://cr.openjdk.java.net/~shade/8031818/webrev.00/
  https://bugs.openjdk.java.net/browse/JDK-8031818

This would be convenient to have in mainline, because it will also
propagate to another arch ports (notably PPC C2 port), and will ease the
performance research for the upcoming JMM update.

Thanks,
-Aleksey.