RFR (S) 8185590: ShouldNotReachHere from ClassLoaderData::try_get_next_class()

[coleen.phillimore at oracle.com]

Summary: Counting number of instanceKlass code didn't work.

A late code review change caused this regression.   Tested with internal 
NSK mlvm tests with -XX:-TieredCompilation -XX:CompileThreshold=100 
including the one where I reproduced the failure overnight.

open webrev at http://cr.openjdk.java.net/~coleenp/8185590.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8185590

Thanks,
Coleen