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

src/execution.cc

Index: src/execution.cc
diff --git a/src/execution.cc b/src/execution.cc
index 7aa4f3341d68a4bfd3c569f4537df3db8593f3a4..ffc6342b709683a20e63b381dd8be19243838c37 100644
--- a/src/execution.cc
+++ b/src/execution.cc
@@ -539,6 +539,12 @@ MaybeHandle<Object> Execution::NewDate(Isolate* isolate, double time) {
 }
 
 
+MaybeHandle<Object> Execution::PromiseHasRejectHandler(Isolate* isolate,
+                                                       Handle<Object> promise) {
+  return Call(isolate, isolate->promise_has_reject_handler(), promise, 0, NULL);
+}
+
+
 #undef RETURN_NATIVE_CALL