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

Source/core/dom/ElementRareData.h

 /*
  * Copyright (C) 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2008 David Smith <catfish.man@gmail.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,
@@ skipping 13 matching lines @@
 
 #include "core/animation/ElementAnimations.h"
 #include "core/dom/Attr.h"
 #include "core/dom/DatasetDOMStringMap.h"
 #include "core/dom/NamedNodeMap.h"
 #include "core/dom/NodeRareData.h"
 #include "core/dom/PseudoElement.h"
 #include "core/dom/custom/CustomElementDefinition.h"
 #include "core/dom/shadow/ElementShadow.h"
 #include "core/html/ClassList.h"
+#include "core/page/scrolling/ScrollStateCallback.h"
 #include "core/style/StyleInheritedData.h"
 #include "platform/heap/Handle.h"
 #include "wtf/OwnPtr.h"
 
 namespace blink {
 
 class HTMLElement;
 
 class ElementRareData : public NodeRareData {
 public:
@@ skipping 70 matching lines @@
     uint32_t decrementProxyCount()
     {
         ASSERT(m_proxyCount);
         return --m_proxyCount;
     }
     uint32_t proxyCount() const { return m_proxyCount; }
 
     void setCustomElementDefinition(PassRefPtrWillBeRawPtr<CustomElementDefinition> definition) { m_customElementDefinition = definition; }
     CustomElementDefinition* customElementDefinition() const { return m_customElementDefinition.get(); }
 
+    void setDistributeScroll(ScrollStateCallback* scrollStateCallback) { m_distributeScroll = scrollStateCallback; }
+
+    ScrollStateCallback* getDistributeScroll() { return m_distributeScroll.get(); }
+
+    void setApplyScroll(ScrollStateCallback* scrollStateCallback) { m_applyScroll = scrollStateCallback; }
+
+    ScrollStateCallback* getApplyScroll() { return m_applyScroll.get(); }
+
     AttrNodeList& ensureAttrNodeList();
     AttrNodeList* attrNodeList() { return m_attrNodeList.get(); }
     void removeAttrNodeList() { m_attrNodeList.clear(); }
 
     DECLARE_TRACE_AFTER_DISPATCH();
 
 private:
     short m_tabindex;
     // As m_proxyCount usually doesn't exceed 10bits (1024), if you want to add some booleans you
     // can steal some bits from m_proxyCount by using bitfields to prevent ElementRareData bloat.
@@ skipping 11 matching lines @@
     OwnPtrWillBeMember<InlineCSSStyleDeclaration> m_cssomWrapper;
 
     RefPtr<ComputedStyle> m_computedStyle;
     RefPtrWillBeMember<CustomElementDefinition> m_customElementDefinition;
 
     RefPtrWillBeMember<PseudoElement> m_generatedBefore;
     RefPtrWillBeMember<PseudoElement> m_generatedAfter;
     RefPtrWillBeMember<PseudoElement> m_generatedFirstLetter;
     RefPtrWillBeMember<PseudoElement> m_backdrop;
 
+    PersistentWillBeMember<ScrollStateCallback> m_applyScroll;
+    PersistentWillBeMember<ScrollStateCallback> m_distributeScroll;

[tdresser, 2015/07/06 20:43:01]

We need to find somewhere else to stash these, as adding 2*sizeof(Persistent) to
every ElementRareData is an unacceptable size increase (according to haraken@).

[Rick Byers, 2015/07/07 21:24:40]

Can we instead have a map somewhere (per Document?) from Element to
ScrollStateCallback?  Maybe something kind of like EventHandlerRegistry?

[tdresser, 2015/07/13 17:36:52]

Per Document / Framehost would introduce a fair bit of unnecessary complexity,
as Elements can be moved between Documents and FrameHosts. We'd need to pass the
callbacks back and forth when elements are moved around. A static map isn't
particularly elegant, but it lets us tie the lifetime to the lifetime of the
Element without inflating ElementRareData, and doesn't introduce much additional
complexity.

Does this seem reasonable?

[haraken, 2015/07/13 23:43:07]

A static map is fine. See how CustomElementObserverMap works. We can do a
similar thing here.

https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

+
     explicit ElementRareData(LayoutObject*);
 };
 
 inline LayoutSize defaultMinimumSizeForResizing()
 {
     return LayoutSize(LayoutUnit::max(), LayoutUnit::max());
 }
 
 inline ElementRareData::ElementRareData(LayoutObject* layoutObject)
     : NodeRareData(layoutObject)
@@ skipping 68 matching lines @@
     case FIRST_LETTER:
         return m_generatedFirstLetter.get();
     default:
         return 0;
     }
 }
 
 } // namespace
 
 #endif // ElementRareData_h