In JDK9, discontinue FollowReferences from reporting references to class signers. This support was likely added because the reference to the signers was in the metadata for classes and not a direct field in the java/lang/Class instance. The signers are not commonly set unless from the protection domain certificates array. Not saving a signers field per java/lang/Class instance will save footprint directly. The JVM will not have a signers field to follow for JVMTI so we would like to remove this uncommonly used callback.

Suggested change is to add an optional capability and only report references to signers in the java heap if this capability is supported.

See: http://cr.openjdk.java.net/~coleenp/jvmti.html