Reland of Clear LifecycleObserver::m_context when LifecycleObserver::contextDestroyed gets called

third_party/WebKit/Source/platform/LifecycleNotifier.h

Index: third_party/WebKit/Source/platform/LifecycleNotifier.h
diff --git a/third_party/WebKit/Source/platform/LifecycleNotifier.h b/third_party/WebKit/Source/platform/LifecycleNotifier.h
index c38d3da0f4337329c21b26c664667324a8b7f593..e03351d51d1eb1e5f8a92db877c7dadab1615a62 100644
--- a/third_party/WebKit/Source/platform/LifecycleNotifier.h
+++ b/third_party/WebKit/Source/platform/LifecycleNotifier.h
@@ -61,9 +61,7 @@
     {
     }
 
-#if DCHECK_IS_ON()
     T* context() { return static_cast<T*>(this); }
-#endif
 
     using ObserverSet = HeapHashSet<WeakMember<Observer>>;
 
@@ -98,8 +96,9 @@
     ObserverSet observers;
     m_observers.swap(observers);
     for (Observer* observer : observers) {
-        ASSERT(observer->lifecycleContext() == context());
+        DCHECK(observer->lifecycleContext() == context());
         observer->contextDestroyed();
+        observer->clearContext();
     }
 }