Simplify lifecycle notifiers and observers.

Source/core/dom/DocumentLifecycleObserver.h

Index: Source/core/dom/DocumentLifecycleObserver.h
diff --git a/Source/core/dom/DocumentLifecycleObserver.h b/Source/core/dom/DocumentLifecycleObserver.h
index e4ece7589ee507935f723c7a3331e7d31b5599e2..228432933722ca78245dcba4a2164fe55b209ae3 100644
--- a/Source/core/dom/DocumentLifecycleObserver.h
+++ b/Source/core/dom/DocumentLifecycleObserver.h
@@ -30,17 +30,18 @@
 
 namespace blink {
 
-template<> void observeContext(Document*, LifecycleObserver<Document>*);
-template<> void unobserveContext(Document*, LifecycleObserver<Document>*);
+class DocumentLifecycleNotifier;
 
-class DocumentLifecycleObserver : public LifecycleObserver<Document> {
+class DocumentLifecycleObserver : public LifecycleObserver<Document, DocumentLifecycleObserver, DocumentLifecycleNotifier> {
 public:
-    explicit DocumentLifecycleObserver(Document*);
-    virtual ~DocumentLifecycleObserver();
     virtual void documentWasDetached() { }
 #if !ENABLE(OILPAN)
     virtual void documentWasDisposed() { }
 #endif
+
+protected:
+    explicit DocumentLifecycleObserver(Document*);
+    virtual ~DocumentLifecycleObserver();
 };
 
 } // namespace blink