RFR(S): 8153764: Add auxiliary method that generates class by class prototype to gc testlibrary

[Kirill Zhaldybin]

Dear all,

Could you please review this fix for JDK-8153764?

It adds a method to generate class by class prototype.
The method is used by a test for 8132718.

WebRev: http://cr.openjdk.java.net/~kzhaldyb/webrevs/JDK-8153764/webrev.01/

CR: https://bugs.openjdk.java.net/browse/JDK-8153764

Thank you.

Regards, Kirill