Use WeakCells in the optimized code map rather than traversing in pause.

src/contexts.h

Index: src/contexts.h
diff --git a/src/contexts.h b/src/contexts.h
index a7bbebf09ffc764b8771ac62e0356e45ceaa672f..179df8b9be69a9dc66d982644963bd52daa77ae2 100644
--- a/src/contexts.h
+++ b/src/contexts.h
@@ -230,6 +230,7 @@ enum BindingFlags {
   V(SCRIPT_CONTEXT_TABLE_INDEX, ScriptContextTable, script_context_table)      \
   V(SCRIPT_FUNCTION_INDEX, JSFunction, script_function)                        \
   V(SECURITY_TOKEN_INDEX, Object, security_token)                              \
+  V(SELF_WEAK_CELL_INDEX, WeakCell, self_weak_cell)                            \
   V(SET_ITERATOR_MAP_INDEX, Map, set_iterator_map)                             \
   V(SHARED_ARRAY_BUFFER_FUN_INDEX, JSFunction, shared_array_buffer_fun)        \
   V(SLOPPY_ARGUMENTS_MAP_INDEX, Map, sloppy_arguments_map)                     \