Introduce DEFINE_ELEMENT_DATA_TYPE_CASTS, and use it

Source/core/dom/ElementData.h

Index: Source/core/dom/ElementData.h
diff --git a/Source/core/dom/ElementData.h b/Source/core/dom/ElementData.h
index f7f4a07996c6b120ea9dc68fa6fa1ba45abd22b0..b34a07e52de91b9e89accf6036f58b0e60ffb6dc 100644
--- a/Source/core/dom/ElementData.h
+++ b/Source/core/dom/ElementData.h
@@ -111,6 +111,9 @@ private:
     PassRefPtrWillBeRawPtr<UniqueElementData> makeUniqueCopy() const;
 };
 
+#define DEFINE_ELEMENT_DATA_TYPE_CASTS(thisType, predicate) \
+    DEFINE_TYPE_CASTS(thisType, ElementData, data, data->isUnique() == predicate, data.isUnique() == predicate)
+
 #if COMPILER(MSVC)
 #pragma warning(push)
 #pragma warning(disable: 4200) // Disable "zero-sized array in struct/union" warning
@@ -145,6 +148,8 @@ public:
     Attribute m_attributeArray[0];
 };
 
+DEFINE_ELEMENT_DATA_TYPE_CASTS(ShareableElementData, false);

[Inactive, 2014/07/21 12:14:00]

nit: I would have introduced a "isShareable()" method and used it here. I find
it not very readable to have a boolean macro parameter here.

+
 #if COMPILER(MSVC)
 #pragma warning(pop)
 #endif
@@ -183,6 +188,8 @@ public:
     Vector<Attribute, 4> m_attributeVector;
 };
 
+DEFINE_ELEMENT_DATA_TYPE_CASTS(UniqueElementData, true);

[Inactive, 2014/07/21 12:14:00]

ditto: s/true/isUnique

+
 #if !ENABLE(OILPAN)
 inline void ElementData::deref()
 {
@@ -196,14 +203,14 @@ 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