RFR(s): 8148945: JDK-8148481: Devirtualize Klass::vtable breaks Zero build

[Severin Gehwolf]

Hi,

Could somebody please review and sponsor this Zero build fix?

JDK-8148481 made start_of_vtable() protected and this change accounts
for that by now using the new method_at_vtable() function. I
think src/share/vm/interpreter/bytecodeInterpreter.cpp is Zero-only
these days even though it lives in shared code.

Bug: https://bugs.openjdk.java.net/browse/JDK-8148945
webrev: http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8148945/webrev.01/

Testing done: Zero builds again in all variants.

Thanks,
Severin