String intern table and support for unordered_map

Change-Id: I22d86d060780552675c5d7f14a98ffde480eac82
diff --git a/src/heap.h b/src/heap.h
index 1059fd7..f8a5d23 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -23,6 +23,8 @@
 
   static const size_t kMaximumSize = 64 * MB;
 
+  typedef void (RootVistor)(Object* root, void* arg);
+
   static bool Init() {
     return Init(kStartupSize, kMaximumSize);
   }