Simplify lifecycle notifiers and observers.

Source/core/dom/ContextLifecycleObserver.h

Index: Source/core/dom/ContextLifecycleObserver.h
diff --git a/Source/core/dom/ContextLifecycleObserver.h b/Source/core/dom/ContextLifecycleObserver.h
index 4bf29e2970b1fefda5aa0c8c4e4c394fa79434f4..19fa6f9c7bb8b4eac6cb90a4003931aba3424f7e 100644
--- a/Source/core/dom/ContextLifecycleObserver.h
+++ b/Source/core/dom/ContextLifecycleObserver.h
@@ -31,15 +31,26 @@
 
 namespace blink {
 
-template<> void observeContext(ExecutionContext*, LifecycleObserver<ExecutionContext>*);
-template<> void unobserveContext(ExecutionContext*, LifecycleObserver<ExecutionContext>*);
+class ContextLifecycleNotifier;
 
-class ContextLifecycleObserver : public LifecycleObserver<ExecutionContext> {
+class ContextLifecycleObserver : public LifecycleObserver<ExecutionContext, ContextLifecycleObserver, ContextLifecycleNotifier> {
 public:
-    explicit ContextLifecycleObserver(ExecutionContext*, Type = GenericType);
     ExecutionContext* executionContext() const { return lifecycleContext(); }
+
+    enum Type {
+        GenericType,
+        ActiveDOMObjectType,
+    };
+
+    Type observerType() const { return m_observerType; }
+
 protected:
+    explicit ContextLifecycleObserver(ExecutionContext*, Type = GenericType);
+
     virtual ~ContextLifecycleObserver();
+
+private:
+    Type m_observerType;
 };
 
 } // namespace blink