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 bd9432c776ebd9cdf97cd39a818737c65925f56c..b888a4a82ccd16d15a4690577bc0b02bc844f338 100644
--- a/src/contexts.h
+++ b/src/contexts.h
@@ -220,6 +220,7 @@ 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)                     \