Simplify lifecycle notifiers and observers.

Source/core/page/Page.h

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2013 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  */
 
 #ifndef Page_h
 #define Page_h
 
 #include "core/dom/ViewportDescription.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/SettingsDelegate.h"
 #include "core/frame/UseCounter.h"
 #include "core/page/PageAnimator.h"
 #include "core/page/PageLifecycleNotifier.h"
+#include "core/page/PageLifecycleObserver.h"
 #include "core/page/PageVisibilityState.h"
 #include "platform/Supplementable.h"
 #include "platform/geometry/LayoutRect.h"
 #include "platform/geometry/Region.h"
 #include "platform/heap/Handle.h"
 #include "wtf/Forward.h"
 #include "wtf/HashSet.h"
 #include "wtf/Noncopyable.h"
 #include "wtf/text/WTFString.h"
 
@@ skipping 225 matching lines @@
     WillBeHeapHashSet<RawPtrWillBeWeakMember<MultisamplingChangedObserver>> m_multisamplingChangedObservers;
 
     // A pointer to all the interfaces provided to in-process Frames for this Page.
     // FIXME: Most of the members of Page should move onto FrameHost.
     OwnPtrWillBeMember<FrameHost> m_frameHost;
 };
 
 } // namespace blink
 
 #endif // Page_h