Remove PageVisibilityObserver contextDestroyed() notifications.

third_party/WebKit/Source/platform/LifecycleContextTest.cpp

 /*
  * Copyright (C) 2013 Google Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 38 matching lines @@
 class TestingObserver final
     : public GarbageCollected<TestingObserver>,
       public LifecycleObserver<DummyContext, TestingObserver> {
   USING_GARBAGE_COLLECTED_MIXIN(TestingObserver);
 
  public:
   static TestingObserver* create(DummyContext* context) {
     return new TestingObserver(context);
   }
 
-  void contextDestroyed(DummyContext* destroyedContext) override {
+  void contextDestroyed(DummyContext* destroyedContext) {
     if (m_observerToRemoveOnDestruct) {
       destroyedContext->removeObserver(m_observerToRemoveOnDestruct);
       m_observerToRemoveOnDestruct.clear();
     }
     m_contextDestroyedCalled = true;
   }
 
   DEFINE_INLINE_TRACE() {
     visitor->trace(m_observerToRemoveOnDestruct);
     LifecycleObserver::trace(visitor);
@@ skipping 59 matching lines @@
 
   context->notifyContextDestroyed();
   EXPECT_EQ(observer->innerObserver(), nullptr);
   context = nullptr;
   ThreadState::current()->collectAllGarbage();
   EXPECT_EQ(observer->lifecycleContext(), static_cast<DummyContext*>(0));
   EXPECT_TRUE(observer->contextDestroyedCalled());
 }
 
 }  // namespace blink