Correctly track lifetime of promise rejection events

Source/bindings/core/v8/custom/V8PromiseRejectionEventCustom.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "bindings/core/v8/V8PromiseRejectionEvent.h"
 
 #include "bindings/core/v8/ScriptPromise.h"
 #include "bindings/core/v8/ScriptState.h"
 #include "bindings/core/v8/ScriptValue.h"
+#include "bindings/core/v8/ScriptWrappable.h"
 #include "bindings/core/v8/V8Binding.h"
 
 namespace blink {
 
 void V8PromiseRejectionEvent::promiseAttributeGetterCustom(const v8::FunctionCallbackInfo<v8::Value>& info)
 {
     v8::Isolate* isolate = info.GetIsolate();
     PromiseRejectionEvent* event = V8PromiseRejectionEvent::toImpl(info.Holder());
     ScriptPromise promise = event->promise(ScriptState::current(isolate));
     if (promise.isEmpty()) {
         v8SetReturnValue(info, v8::Null(isolate));
         return;
     }
 
     v8SetReturnValue(info, promise.v8Value());
 }
 
+void V8PromiseRejectionEvent::visitDOMWrapper(v8::Isolate* isolate, ScriptWrappable* scriptWrappable, const v8::Persistent<v8::Object>& wrapper)
+{
+    PromiseRejectionEvent* event = scriptWrappable->toImpl<PromiseRejectionEvent>();
+    event->setWrapperReference(isolate, wrapper);
+}
+
 } // namespace blink