Disallow adding ContextLifecycleObservers during iteration.

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 43 matching lines @@
 class TestingObserver final : public NoBaseWillBeGarbageCollectedFinalized<TestingObserver>, public LifecycleObserver<DummyContext, TestingObserver, DummyContext> {
     WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(TestingObserver);
 public:
     static PassOwnPtrWillBeRawPtr<TestingObserver> create(DummyContext* context)
     {
         return adoptPtrWillBeNoop(new TestingObserver(context));
     }
 
     virtual void contextDestroyed() override
     {
-        LifecycleObserver<DummyContext, TestingObserver, DummyContext>::contextDestroyed();
+        LifecycleObserver::contextDestroyed();
         if (m_observerToRemoveOnDestruct) {
             lifecycleContext()->removeObserver(m_observerToRemoveOnDestruct.get());
             m_observerToRemoveOnDestruct.clear();
         }
         m_contextDestroyedCalled = true;
     }
 
     DEFINE_INLINE_TRACE()
     {
         visitor->trace(m_observerToRemoveOnDestruct);
-        LifecycleObserver<DummyContext, TestingObserver, DummyContext>::trace(visitor);
+        LifecycleObserver::trace(visitor);
     }
 
     void unobserve() { setContext(nullptr); }
 
     void setObserverToRemoveAndDestroy(PassOwnPtrWillBeRawPtr<TestingObserver> observerToRemoveOnDestruct)
     {
         ASSERT(!m_observerToRemoveOnDestruct);
         m_observerToRemoveOnDestruct = observerToRemoveOnDestruct;
     }
 
     TestingObserver* innerObserver() const { return m_observerToRemoveOnDestruct.get(); }
     bool contextDestroyedCalled() const { return m_contextDestroyedCalled; }
 
 private:
     explicit TestingObserver(DummyContext* context)
-        : m_contextDestroyedCalled(false)
+        : LifecycleObserver(context)
+        , m_contextDestroyedCalled(false)
     {
-        setContext(context);
     }
 
     OwnPtrWillBeMember<TestingObserver> m_observerToRemoveOnDestruct;
     bool m_contextDestroyedCalled;
 };
 
 TEST(LifecycleContextTest, shouldObserveContextDestroyed)
 {
     OwnPtrWillBeRawPtr<DummyContext> context = DummyContext::create();
     OwnPtrWillBePersistent<TestingObserver> observer = TestingObserver::create(context.get());
@@ skipping 37 matching lines @@
 
     context->notifyContextDestroyed();
     EXPECT_EQ(observer->innerObserver(), nullptr);
     context = nullptr;
     Heap::collectAllGarbage();
     EXPECT_EQ(observer->lifecycleContext(), static_cast<DummyContext*>(0));
     EXPECT_TRUE(observer->contextDestroyedCalled());
 }
 
 } // namespace blink