[wrapper-tracing] Fix leak in RemotePlayback round 2

third_party/WebKit/Source/modules/remoteplayback/RemotePlayback.cpp

 // Copyright 2016 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 "modules/remoteplayback/RemotePlayback.h"
 
 #include "bindings/core/v8/ScriptPromiseResolver.h"
 #include "bindings/modules/v8/RemotePlaybackAvailabilityCallback.h"
 #include "core/HTMLNames.h"
 #include "core/dom/DOMException.h"
@@ skipping 184 matching lines @@
   return remotePlaybackStateToString(m_state);
 }
 
 bool RemotePlayback::hasPendingActivity() const {
   return hasEventListeners() || !m_availabilityCallbacks.isEmpty() ||
          m_promptPromiseResolver;
 }
 
 void RemotePlayback::contextDestroyed() {
   m_availabilityCallbacks.clear();
+  m_promptPromiseResolver = nullptr;
 }
 
 void RemotePlayback::notifyInitialAvailability(int callbackId) {
   // May not find the callback if the website cancels it fast enough.
   auto iter = m_availabilityCallbacks.find(callbackId);
   if (iter == m_availabilityCallbacks.end())
     return;
 
   iter->value->call(this, remotePlaybackAvailable());
 }
@@ skipping 92 matching lines @@
 }
 
 DEFINE_TRACE_WRAPPERS(RemotePlayback) {
   for (auto callback : m_availabilityCallbacks.values()) {
     visitor->traceWrappers(callback);
   }
   EventTargetWithInlineData::traceWrappers(visitor);
 }
 
 }  // namespace blink