RFR (S): 8198561: Make oop and narrowOop always have their own class type

[Kim Barrett]

> On Feb 27, 2018, at 9:45 AM, Erik Österlund <erik.osterlund at oracle.com> wrote:
> 
> Hi Kim,
> 
> Thank you for looking at this.
> 
> New full webrev covering all comments so far (hopefully):
> http://cr.openjdk.java.net/~eosterlund/8198561/webrev.01/
> 
> Incremental webrev:
> http://cr.openjdk.java.net/~eosterlund/8198561/webrev.00_01/

So we have implicit conversions from PrimitiveType to narrowOop, and
that allows implicit narrowing conversions from other integral types
to PrimitiveType.  It would be nice to poison the implicit narrowing
conversions, but maybe VS implicit narrowing warnings are sufficient
for that?  And eventual -Wconversion for gcc; see JDK-8135181.

Looks good.