8027454: Do not traverse string table during G1 remark when treating them as...

8027454: Do not traverse string table during G1 remark when treating them as strong roots during initial mark
Summary: Do not try to unlink string table entries unconditionally during remark. This is without side effects as the preceding initial mark always uses the string table as strong roots. Needs to be fixed with class unloading during concurrent mark.
Reviewed-by: brutisso, mgerdin

src/share/vm/gc_implementation/g1/concurrentMark.cpp

@@ -2528,7 +2528,9 @@ void ConcurrentMark::weakRefsWork(bool clear_all_soft_refs) {
     assert(!rp->discovery_enabled(), "Post condition");
   }
 
-  g1h->unlink_string_and_symbol_table(&g1_is_alive);
+  g1h->unlink_string_and_symbol_table(&g1_is_alive,
+                                      /* process_strings */ false, // currently strings are always roots
+                                      /* process_symbols */ true);
 }
 
 void ConcurrentMark::swapMarkBitMaps() {