RFR(XS): 8132980: Improve stability of whitebox methods getCodeBlob and freeCodeBlob

[Kirill Zhaldybin]

Hi!

Could you please review the following patch for WB methods?

I added checks for negative size and null address values (where 
applicable) for getCodeBlob, allocateCodeBlob and freeCodeBlob, added 
regression test.

CR:
https://bugs.openjdk.java.net/browse/JDK-8132980
Webrev:
hotspot: http://cr.openjdk.java.net/~kzhaldyb/webrevs/JDK-8132980/webrev.00/

Thanks,
Kirill