RFR(M): 8194490: [JVMCI] Move `iterateFrames` to C++

[Gilles Duboscq]

Hi,

Please review the following fix for `HotSpotStackIntrospection.iterateFrames`.
It moves the iteration code from Java to C++: this helps with an issue that would arise if the nmethod containing the `iterateFrames` hits and uncommon trap during iteration. IT would change the layout of the top frames which would confuse the stack walking logic. Having this loop in C++ ensure there can be no uncommon trap.

Webrev: http://cr.openjdk.java.net/~gdub/webrev-8194490/
Issue: https://bugs.openjdk.java.net/browse/JDK-8194490
Testing: hs-tier1,hs-tier2,hs-precheckin-comp

It's bit unfortunate that we have tests for implementation details of JVMCI (i.e., tests for CompilerToVM) instead of tests for the actual API.

Thanks,
 Gilles