RFR(M): 8209420: Track membars for volatile accesses so they can be properly optimized

[Roland Westrelin]

Hi Tobias,

> I've submitted some testing and the build fails on Sparc due to:

Thanks for doing that.

Here is a new webrev:

http://cr.openjdk.java.net/~roland/8209420/webrev.01/

It removes the trailing comma and adds an assert that barriers are only
removed for non escaping objects (as discussed with Andrew D.).

I ran it through the submit repo and it passed.

Roland.