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

src/runtime/runtime.cc

Index: src/runtime/runtime.cc
diff --git a/src/runtime/runtime.cc b/src/runtime/runtime.cc
index 379a38f746d7f5bcbb00bd06607f8d69cb1a3fef..d562da5947223f8e18f5ecb9f8c5d69c8fc88c11 100644
--- a/src/runtime/runtime.cc
+++ b/src/runtime/runtime.cc
@@ -5341,12 +5341,19 @@ RUNTIME_FUNCTION(Runtime_DebugPromiseEvent) {
 }
 
 
-RUNTIME_FUNCTION(Runtime_DebugPromiseRejectEvent) {
+RUNTIME_FUNCTION(Runtime_PromiseRejectEvent) {
   DCHECK(args.length() == 2);
   HandleScope scope(isolate);
   CONVERT_ARG_HANDLE_CHECKED(JSObject, promise, 0);
   CONVERT_ARG_HANDLE_CHECKED(Object, value, 1);
-  isolate->debug()->OnPromiseReject(promise, value);
+  // Check whether the promise has been marked as having triggered a message.
+  Handle<Symbol> key = isolate->factory()->promise_debug_symbol();
+  Maybe<bool> marked = JSObject::HasOwnProperty(promise, key);
+  DCHECK(marked.has_value);
+  if (!marked.value) {
+    isolate->debug()->OnPromiseReject(promise, value);
+    isolate->ReportPromiseReject(promise, value, NULL);
+  }
   return isolate->heap()->undefined_value();
 }