Viewport apply scroll should be on the document element not scrollingElement.

third_party/WebKit/Source/core/dom/Document.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
@@ skipping 1140 matching lines @@
 
     void setHoverNode(Node*);
 
     using EventFactorySet = HashSet<OwnPtr<EventFactoryBase>>;
     static EventFactorySet& eventFactories();
 
     void setNthIndexCache(NthIndexCache* nthIndexCache) { DCHECK(!m_nthIndexCache || !nthIndexCache); m_nthIndexCache = nthIndexCache; }
 
     const OriginAccessEntry& accessEntryFromURL();
 
-    // Installs the viewport scrolling callback (the "applyScroll" in Scroll
-    // Customization lingo) on the root scrollingElement. This callback is
-    // responsible for viewport related scroll actions like top controls
-    // movement and overscroll glow as well as actually scrolling the root
-    // viewport.
-    void updateViewportApplyScroll();
-
     DocumentLifecycle m_lifecycle;
 
     bool m_hasNodesWithPlaceholderStyle;
     bool m_evaluateMediaQueriesOnStyleRecalc;
 
     // If we do ignore the pending stylesheet count, then we need to add a boolean
     // to track that this happened so that we can do a full repaint when the stylesheets
     // do eventually load.
     PendingSheetLayout m_pendingSheetLayout;
 
@@ skipping 86 matching lines @@
     String m_rawTitle;
     Member<Element> m_titleElement;
 
     Member<AXObjectCache> m_axObjectCache;
     Member<DocumentMarkerController> m_markers;
 
     Timer<Document> m_updateFocusAppearanceTimer;
 
     Member<Element> m_cssTarget;
 
-    // Not a WeakMember since we want to keep the scrollingElement around until
-    // we move its ApplyScroll onto the new scrollingElement.
-    Member<Element> m_oldScrollingElement;
-
     LoadEventProgress m_loadEventProgress;
 
     double m_startTime;
 
     Member<ScriptRunner> m_scriptRunner;
 
     HeapVector<Member<HTMLScriptElement>> m_currentScriptStack;
 
     OwnPtr<TransformSource> m_transformSource;
 
@@ skipping 154 matching lines @@
 DEFINE_TYPE_CASTS(TreeScope, Document, document, true, true);
 
 } // namespace blink
 
 #ifndef NDEBUG
 // Outside the WebCore namespace for ease of invocation from gdb.
 CORE_EXPORT void showLiveDocumentInstances();
 #endif
 
 #endif // Document_h