Report promise reject with no handler (behind a flag).

src/execution.h

Index: src/execution.h
diff --git a/src/execution.h b/src/execution.h
index 89175cd906d80a9533a47013ba2f0ec129b67fdf..8f2497ddbd4cf9010183285c77586d2dd7782d14 100644
--- a/src/execution.h
+++ b/src/execution.h
@@ -85,6 +85,9 @@ class Execution FINAL : public AllStatic {
   MUST_USE_RESULT static MaybeHandle<Object> NewDate(
       Isolate* isolate, double time);
 
+  MUST_USE_RESULT static MaybeHandle<Object> PromiseHasRejectHandler(
+      Isolate* isolate, Handle<Object> promise);
+
   // Create a new regular expression object from 'pattern' and 'flags'.
   MUST_USE_RESULT static MaybeHandle<JSRegExp> NewJSRegExp(
       Handle<String> pattern, Handle<String> flags);