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

Source/core/page/PageLifecycleNotifier.h

Index: Source/core/page/PageLifecycleNotifier.h
diff --git a/Source/core/page/PageLifecycleNotifier.h b/Source/core/page/PageLifecycleNotifier.h
index 9c28c6731e14b984b42aea76ae3cb3e00dcde310..a9dddbffd03400d5f4d61afeb46dfd7569a33fba 100644
--- a/Source/core/page/PageLifecycleNotifier.h
+++ b/Source/core/page/PageLifecycleNotifier.h
@@ -26,33 +26,52 @@
 #ifndef PageLifecycleNotifier_h
 #define PageLifecycleNotifier_h
 
+#include "core/page/Page.h"
+#include "core/page/PageLifecycleObserver.h"
 #include "platform/LifecycleNotifier.h"
-#include "wtf/HashSet.h"
 #include "wtf/PassOwnPtr.h"
 #include "wtf/TemporaryChange.h"
 
 namespace blink {
 
 class LocalFrame;
-class Page;
-class PageLifecycleObserver;
 
-class PageLifecycleNotifier : public LifecycleNotifier<Page> {
+class PageLifecycleNotifier final : public LifecycleNotifier<Page> {
 public:
+    static PassOwnPtr<PageLifecycleNotifier> create(Page*);
+
     void notifyPageVisibilityChanged();
     void notifyDidCommitLoad(LocalFrame*);
 
     virtual void addObserver(Observer*) override;
     virtual void removeObserver(Observer*) override;
 
-protected:
+private:
     explicit PageLifecycleNotifier(Page*);
 
-private:
     using PageObserverSet = HashSet<PageLifecycleObserver*>;
     PageObserverSet m_pageObservers;
 };
 
+inline PassOwnPtr<PageLifecycleNotifier> PageLifecycleNotifier::create(Page* context)
+{
+    return adoptPtr(new PageLifecycleNotifier(context));
+}
+
+inline void PageLifecycleNotifier::notifyPageVisibilityChanged()
+{
+    TemporaryChange<IterationType> scope(this->m_iterating, IteratingOverPageObservers);
+    for (PageLifecycleObserver* pageObserver : m_pageObservers)
+        pageObserver->pageVisibilityChanged();
+}
+
+inline void PageLifecycleNotifier::notifyDidCommitLoad(LocalFrame* frame)
+{
+    TemporaryChange<IterationType> scope(this->m_iterating, IteratingOverPageObservers);
+    for (PageLifecycleObserver* pageObserver : m_pageObservers)
+        pageObserver->didCommitLoad(frame);
+}
+
 } // namespace blink
 
 #endif // PageLifecycleNotifier_h