Introduce DEFINE_ELEMENT_DATA_TYPE_CASTS, and use it

Source/core/dom/ElementData.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  * Copyright (C) 2014 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 60 matching lines @@
     const StylePropertySet* presentationAttributeStyle() const;
 
     AttributeCollection attributes() const;
 
     bool hasID() const { return !m_idForStyleResolution.isNull(); }
     bool hasClass() const { return !m_classNames.isNull(); }
 
     bool isEquivalent(const ElementData* other) const;
 
     bool isUnique() const { return m_isUnique; }
+    bool isShareable() const { return !m_isUnique; }
 
     void traceAfterDispatch(Visitor*);
     void trace(Visitor*);
 
 protected:
     ElementData();
     explicit ElementData(unsigned arraySize);
     ElementData(const ElementData&, bool isUnique);
 
     // Keep the type in a bitfield instead of using virtual destructors to avoid adding a vtable.
@@ skipping 13 matching lines @@
     friend class UniqueElementData;
     friend class SVGElement;
 
 #if !ENABLE(OILPAN)
     void destroy();
 #endif
 
     PassRefPtrWillBeRawPtr<UniqueElementData> makeUniqueCopy() const;
 };
 
+#define DEFINE_ELEMENT_DATA_TYPE_CASTS(thisType, predicate) \
+    template<typename T> inline thisType* to##thisType(const RefPtr<T>& data) { return to##thisType(data.get()); } \

[Inactive, 2014/07/21 19:37:47]

Sorry, I thought the macro was doing this for us already. If it doesn't, it may
be on purpose (people might find it confusing that a toX() calls converts a
smart pointer into a raw one). My proposal would be to not add it.

Also, why not use DEFINE_TYPE_CASTS() directly instead of having this
intermediate macro? It would probably make introducing isShareable() useless as
we could likely use:
DEFINE_TYPE_CASTS(ShareableElementData, ElementData, data, !data->isUnique(),
!data.isUnique());

[gyuyoung-inactive, 2014/07/22 00:20:32]

I removed .get() in issue 401553002 as well. I would like to ask this to Kent
because he suggested to use it. Kent, what do you think ?
Personally I think intermediate macro is more easier to use. I would like to ask
this to Kent too.

[Inactive, 2014/07/22 00:44:29]

Ok, I see tkent's comment on the other CL, fine then. I don't really mind the
intermediate macro, especially now that we have the RefPtr helper. However, I
still think it would be nice if we did not have to introduce a isShareable()
method, just for this helper.

[tkent, 2014/07/22 00:57:12]

I agree with Chris.  Adding the intermediate macro is ok, but I feel adding
isShareable is unnecessary.

+    DEFINE_TYPE_CASTS(thisType, ElementData, data, data->predicate, data.predicate)
+
 #if COMPILER(MSVC)
 #pragma warning(push)
 #pragma warning(disable: 4200) // Disable "zero-sized array in struct/union" warning
 #endif
 
 // SharableElementData is managed by ElementDataCache and is produced by
 // the parser during page load for elements that have identical attributes. This
 // is a memory optimization since it's very common for many elements to have
 // duplicate sets of attributes (ex. the same classes).
 class ShareableElementData FINAL : public ElementData {
@@ skipping 14 matching lines @@
     void* operator new(std::size_t, void* location)
     {
         return location;
     }
 
     AttributeCollection attributes() const;
 
     Attribute m_attributeArray[0];
 };
 
+DEFINE_ELEMENT_DATA_TYPE_CASTS(ShareableElementData, isShareable());
+
 #if COMPILER(MSVC)
 #pragma warning(pop)
 #endif
 
 // UniqueElementData is created when an element needs to mutate its attributes
 // or gains presentation attribute style (ex. width="10"). It does not need to
 // be created to fill in values in the ElementData that are derived from
 // attributes. For example populating the m_inlineStyle from the style attribute
 // doesn't require a UniqueElementData as all elements with the same style
 // attribute will have the same inline style.
@@ skipping 18 matching lines @@
     void traceAfterDispatch(Visitor*);
 
     // FIXME: We might want to support sharing element data for elements with
     // presentation attribute style. Lots of table cells likely have the same
     // attributes. Most modern pages don't use presentation attributes though
     // so this might not make sense.
     mutable RefPtrWillBeMember<StylePropertySet> m_presentationAttributeStyle;
     Vector<Attribute, 4> m_attributeVector;
 };
 
+DEFINE_ELEMENT_DATA_TYPE_CASTS(UniqueElementData, isUnique());
+
 #if !ENABLE(OILPAN)
 inline void ElementData::deref()
 {
     if (!derefBase())
         return;
     destroy();
 }
 #endif
 
 inline const StylePropertySet* ElementData::presentationAttributeStyle() const
 {
     if (!m_isUnique)
         return 0;
-    return static_cast<const UniqueElementData*>(this)->m_presentationAttributeStyle.get();
+    return toUniqueElementData(this)->m_presentationAttributeStyle.get();
 }
 
 inline AttributeCollection ElementData::attributes() const
 {
     if (isUnique())
-        return static_cast<const UniqueElementData*>(this)->attributes();
-    return static_cast<const ShareableElementData*>(this)->attributes();
+        return toUniqueElementData(this)->attributes();
+    return toShareableElementData(this)->attributes();
 }
 
 inline AttributeCollection ShareableElementData::attributes() const
 {
     return AttributeCollection(m_attributeArray, m_arraySize);
 }
 
 inline AttributeCollection UniqueElementData::attributes() const
 {
     return AttributeCollection(m_attributeVector.data(), m_attributeVector.size());
@@ skipping 10 matching lines @@
 }
 
 inline Attribute& UniqueElementData::attributeAt(unsigned index)
 {
     return m_attributeVector.at(index);
 }
 
 } // namespace blink
 
 #endif // ElementData_h