RFR: 8202230: Provide accessors for JNIHandles storage objects

[coleen.phillimore at oracle.com]

Looks good.
Coleen

On 4/25/18 5:09 PM, Kim Barrett wrote:
> Please review this addition to JNIHandles, providing access to the
> OopStorage objects used to manage the global and weak global handles.
> The accessors assert the storage objects have been allocated.
>
> Also changed direct uses of the storage object variables to instead
> use the new accessors, to get the initialization asserts during
> development.
>
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8202230
>
> Webrev:
> http://cr.openjdk.java.net/~kbarrett/8202230/open.00/
>
> Testing:
> {jdk,hs}-tier{1,2,3} for all Oracle platforms.
>