Start using String type info:

src/type-info.h

Index: src/type-info.h
diff --git a/src/type-info.h b/src/type-info.h
index 1d82634092c5eaf121baf70ad536b0d5f51e3cf0..568437a9cee11bb4615e2a020beefe70c15f0f4f 100644
--- a/src/type-info.h
+++ b/src/type-info.h
@@ -156,6 +156,11 @@ class TypeInfo {
     return ((type_ & kDoubleType) == kDoubleType);
   }
 
+  inline bool IsString() {
+    ASSERT(type_ != kUninitializedType);
+    return ((type_ & kStringType) == kStringType);
+  }
+
   inline bool IsUninitialized() {
     return type_ == kUninitializedType;
   }