Introduce PromiseRejectCallback.

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index 63ea457cec3c1e75db81b4922f685073f1f66055..54b7d350dc7c47072af6b4df1939acf30cb6c1d5 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -5985,6 +5985,16 @@ Local<Promise> Promise::Then(Handle<Function> handler) {
 }
 
 
+bool Promise::HasRejectHandler() {
+  i::Handle<i::JSObject> promise = Utils::OpenHandle(this);
+  i::Isolate* isolate = promise->GetIsolate();
+  LOG_API(isolate, "Promise::HasRejectHandler");
+  ENTER_V8(isolate);
+  i::Handle<i::Symbol> key = isolate->factory()->promise_has_handler_symbol();
+  return i::JSObject::GetDataProperty(promise, key)->IsTrue();
+}
+
+
 bool v8::ArrayBuffer::IsExternal() const {
   return Utils::OpenHandle(this)->is_external();
 }
@@ -6732,6 +6742,13 @@ void Isolate::RemoveCallCompletedCallback(CallCompletedCallback callback) {
 }
 
 
+void Isolate::SetPromiseRejectCallback(PromiseRejectCallback callback) {
+  if (callback == NULL) return;
+  i::Isolate* isolate = reinterpret_cast<i::Isolate*>(this);
+  isolate->SetPromiseRejectCallback(callback);
+}
+
+
 void Isolate::RunMicrotasks() {
   reinterpret_cast<i::Isolate*>(this)->RunMicrotasks();
 }