6863023: need non-perm oops in code cache for JSR 292

Make a special root-list for those few nmethods which might contain non-perm oops.

Reviewed-by: twisti, kvn, never, jmasa, ysr

hotspot/src/share/vm/code/codeBlob.hpp

@@ -175,6 +175,8 @@ class CodeBlob VALUE_OBJ_CLASS_SPEC {
                             OopClosure* keep_alive,
                             bool unloading_occurred);
   virtual void oops_do(OopClosure* f) = 0;
+  // (All CodeBlob subtypes other than NMethod currently have
+  // an empty oops_do() method.
 
   // OopMap for frame
   OopMapSet* oop_maps() const                    { return _oop_maps; }