Revert "Revert "Hold dex caches live in class table""

Bug: 29083330

This reverts commit f102faf1bcbdb2149e3e7bf27b1819f621b7894b.

Change-Id: Ibc6d260247b3113beec7d33552061512a36c9ce8
diff --git a/runtime/class_table-inl.h b/runtime/class_table-inl.h
index 42e320a..d52365d 100644
--- a/runtime/class_table-inl.h
+++ b/runtime/class_table-inl.h
@@ -29,7 +29,7 @@
       visitor.VisitRoot(root.AddressWithoutBarrier());
     }
   }
-  for (GcRoot<mirror::Object>& root : dex_files_) {
+  for (GcRoot<mirror::Object>& root : strong_roots_) {
     visitor.VisitRoot(root.AddressWithoutBarrier());
   }
 }
@@ -42,7 +42,7 @@
       visitor.VisitRoot(root.AddressWithoutBarrier());
     }
   }
-  for (GcRoot<mirror::Object>& root : dex_files_) {
+  for (GcRoot<mirror::Object>& root : strong_roots_) {
     visitor.VisitRoot(root.AddressWithoutBarrier());
   }
 }