Presentation API: ignore page visibility changes if ExecutionContext is destoyed.

Source/modules/presentation/PresentationAvailability.cpp

 // Copyright 2014 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 "modules/presentation/PresentationAvailability.h"
 
 #include "bindings/core/v8/ScriptPromiseResolver.h"
 #include "core/dom/Document.h"
 #include "core/events/Event.h"
@@ skipping 85 matching lines @@
     setState(State::Suspended);
 }
 
 void PresentationAvailability::stop()
 {
     setState(State::Inactive);
 }
 
 void PresentationAvailability::pageVisibilityChanged()
 {
+    if (m_state == State::Inactive)
+        return;
     updateListening();
 }
 
 void PresentationAvailability::setState(State state)
 {
     m_state = state;
     updateListening();
 }
 
 void PresentationAvailability::updateListening()
@@ skipping 18 matching lines @@
     return m_value;
 }
 
 DEFINE_TRACE(PresentationAvailability)
 {
     RefCountedGarbageCollectedEventTargetWithInlineData<PresentationAvailability>::trace(visitor);
     PageLifecycleObserver::trace(visitor);
     ActiveDOMObject::trace(visitor);
 }
 
-} // namespace
+} // blink namespace