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

src/factory.cc

Index: src/factory.cc
diff --git a/src/factory.cc b/src/factory.cc
index 0adc8730f5f31b01dc406963988bed5ad7005390..d52c151c47da7fde6c0db25e038fbe690d91a412 100644
--- a/src/factory.cc
+++ b/src/factory.cc
@@ -1930,11 +1930,8 @@ Handle<SharedFunctionInfo> Factory::NewSharedFunctionInfo(
 
 
 Handle<JSMessageObject> Factory::NewJSMessageObject(
-    Handle<String> type,
-    Handle<JSArray> arguments,
-    int start_position,
-    int end_position,
-    Handle<Object> script,
+    Handle<String> type, Handle<JSArray> arguments, Handle<Object> promise,
+    int start_position, int end_position, Handle<Object> script,
     Handle<Object> stack_frames) {
   Handle<Map> map = message_object_map();
   Handle<JSMessageObject> message = New<JSMessageObject>(map, NEW_SPACE);
@@ -1943,6 +1940,7 @@ Handle<JSMessageObject> Factory::NewJSMessageObject(
   message->set_elements(*empty_fixed_array(), SKIP_WRITE_BARRIER);
   message->set_type(*type);
   message->set_arguments(*arguments);
+  message->set_promise(*promise);
   message->set_start_position(start_position);
   message->set_end_position(end_position);
   message->set_script(*script);