Revert r189385 "Remove LifecycleContext" and r189391, r189530, r189456 that block it

Source/core/dom/DocumentLifecycleObserver.cpp

Index: Source/core/dom/DocumentLifecycleObserver.cpp
diff --git a/Source/core/dom/DocumentLifecycleObserver.cpp b/Source/core/dom/DocumentLifecycleObserver.cpp
index f6093d96037cea03a8203ec468186af03a990d7d..78771725e0f92d1fb63aa67f1b2aef43b9a37bc1 100644
--- a/Source/core/dom/DocumentLifecycleObserver.cpp
+++ b/Source/core/dom/DocumentLifecycleObserver.cpp
@@ -28,18 +28,17 @@
 #include "core/dom/DocumentLifecycleObserver.h"
 
 #include "core/dom/Document.h"
-#include "core/dom/DocumentLifecycleNotifier.h"
 
 namespace blink {
 
-template<> void observeContext(Document* context, LifecycleObserver<Document>* observer)
+template<> void observerContext(Document* context, LifecycleObserver<Document>* observer)
 {
-    static_cast<DocumentLifecycleNotifier*>(context)->addObserver(observer);
+    static_cast<LifecycleContext<Document>*>(context)->wasObservedBy(observer);
 }
 
-template<> void unobserveContext(Document* context, LifecycleObserver<Document>* observer)
+template<> void unobserverContext(Document* context, LifecycleObserver<Document>* observer)
 {
-    static_cast<DocumentLifecycleNotifier*>(context)->removeObserver(observer);
+    static_cast<LifecycleContext<Document>*>(context)->wasUnobservedBy(observer);
 }
 
 DocumentLifecycleObserver::DocumentLifecycleObserver(Document* document)