Introduce and use type casting functions for several HTMLCollection types

Source/core/html/HTMLCollection.cpp

Index: Source/core/html/HTMLCollection.cpp
diff --git a/Source/core/html/HTMLCollection.cpp b/Source/core/html/HTMLCollection.cpp
index 79bb5313c1683fd942be761d22b421a8b4c591e2..61c63c894218c6f3443aa8d4c4fa0e37d352e18a 100644
--- a/Source/core/html/HTMLCollection.cpp
+++ b/Source/core/html/HTMLCollection.cpp
@@ -201,11 +201,11 @@ template <> inline bool isMatchingElement(const HTMLCollection& htmlCollection,
     case NodeChildren:
         return true;
     case ClassCollectionType:
-        return static_cast<const ClassCollection&>(htmlCollection).elementMatches(element);
+        return toClassCollection(htmlCollection).elementMatches(element);
     case TagCollectionType:
-        return static_cast<const TagCollection&>(htmlCollection).elementMatches(element);
+        return toTagCollection(htmlCollection).elementMatches(element);
     case HTMLTagCollectionType:
-        return static_cast<const HTMLTagCollection&>(htmlCollection).elementMatches(element);
+        return toHTMLTagCollection(htmlCollection).elementMatches(element);
     default:
         break;
     }
@@ -339,9 +339,9 @@ Element* HTMLCollection::traverseToFirstElement() const
 {
     switch (type()) {
     case HTMLTagCollectionType:
-        return firstMatchingElement(static_cast<const HTMLTagCollection&>(*this));
+        return firstMatchingElement(toHTMLTagCollection(*this));
     case ClassCollectionType:
-        return firstMatchingElement(static_cast<const ClassCollection&>(*this));
+        return firstMatchingElement(toClassCollection(*this));
     default:
         if (overridesItemAfter())
             return virtualItemAfter(0);
@@ -373,9 +373,9 @@ Element* HTMLCollection::traverseForwardToOffset(unsigned offset, Element& curre
     ASSERT(currentOffset < offset);
     switch (type()) {
     case HTMLTagCollectionType:
-        return traverseMatchingElementsForwardToOffset(static_cast<const HTMLTagCollection&>(*this), offset, currentElement, currentOffset);
+        return traverseMatchingElementsForwardToOffset(toHTMLTagCollection(*this), offset, currentElement, currentOffset);
     case ClassCollectionType:
-        return traverseMatchingElementsForwardToOffset(static_cast<const ClassCollection&>(*this), offset, currentElement, currentOffset);
+        return traverseMatchingElementsForwardToOffset(toClassCollection(*this), offset, currentElement, currentOffset);
     default:
         if (overridesItemAfter()) {
             Element* next = &currentElement;