Expose scroll customization for touch to JS (behind REF).

Source/core/dom/Document.cpp

 /*
  * 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, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) Research In Motion Limited 2010-2011. All rights reserved.
@@ skipping 2674 matching lines @@
     }
 
     if (!m_frame)
         return;
 
     // Don't remove event listeners from a transitional empty document (see https://bugs.webkit.org/show_bug.cgi?id=28716 for more information).
     bool keepEventListeners = m_frame->loader().stateMachine()->isDisplayingInitialEmptyDocument() && m_frame->loader().provisionalDocumentLoader()
         && isSecureTransitionTo(m_frame->loader().provisionalDocumentLoader()->url());
     if (!keepEventListeners)
         removeAllEventListenersRecursively();
+    if (RuntimeEnabledFeatures::scrollCustomizationEnabled())
+        Element::removeScrollCustomizationCallbacksForDocument(this);

[haraken, 2015/08/13 23:42:05]

Why do we need to remove callbacks in dispatchUnloadEvents()? Wouldn't it be
enough to let each Element's destructor remove the callback with
removeCallbacksForElement?

 }
 
 Document::PageDismissalType Document::pageDismissalEventBeingDispatched() const
 {
     if (m_loadEventProgress == BeforeUnloadEventInProgress)
         return BeforeUnloadDismissal;
     if (m_loadEventProgress == PageHideInProgress)
         return PageHideDismissal;
     if (m_loadEventProgress == UnloadEventInProgress)
         return UnloadDismissal;
@@ skipping 3076 matching lines @@
 #ifndef NDEBUG
 using namespace blink;
 void showLiveDocumentInstances()
 {
     WeakDocumentSet& set = liveDocumentSet();
     fprintf(stderr, "There are %u documents currently alive:\n", set.size());
     for (Document* document : set)
         fprintf(stderr, "- Document %p URL: %s\n", document, document->url().string().utf8().data());
 }
 #endif