Add three string constants from parser to the root-set.

src/heap.h

Index: src/heap.h
diff --git a/src/heap.h b/src/heap.h
index cb421d471b3cb046afcf4e67bb5b6fbdf5116eb3..d15a51c16d4d9215681ac70586e4bd2a71151ac0 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -209,8 +209,10 @@ namespace internal {
   V(Boolean_string, "Boolean")                                           \
   V(callee_string, "callee")                                             \
   V(constructor_string, "constructor")                                   \
-  V(result_string, ".result")                                            \
+  V(dot_result_string, ".result")                                        \
   V(dot_for_string, ".for.")                                             \
+  V(dot_iterator_string, ".iterator")                                    \
+  V(dot_generator_object_string, ".generator_object")                    \
   V(eval_string, "eval")                                                 \
   V(empty_string, "")                                                    \
   V(function_string, "function")                                         \