RFR (S) 8057570: RedefineClasses() tests fail assert(((Metadata*)obj)->is_valid()) failed: obj ,is valid

[Coleen Phillimore]

Summary: Revert two small changes from the previous-versions cleanup 
with marking code cache.

These weren't really related to the cleanup, but I thought they'd make 
it more efficient.  One caused the crash and the other I'm just being 
paranoid about.  Remind me to stay away from deoptimization.

open webrev at http://cr.openjdk.java.net/~coleenp/8057570/
bug link https://bugs.openjdk.java.net/browse/JDK-8057570

Tested with failing test case in loop on machine where it failed every time.

Coleen