RFR 8159010: [JVMCI] crashes with class redefinition

[Tom Rodriguez]

http://cr.openjdk.java.net/~never/8159010/webrev

Running Graal with the VisualVM profiler resulted in some crashes.  The profiler is based on the netbeans one that performs redefinition as part of the profiling.  The primary problem was that ConstantPools weren’t being registered for metadata scanning.  Additionally the logic that trimmed the list of WeakReferences was truncating the list because the iterator was incorrect.

tom