Use new Traversal<> API more in the code base

Source/core/dom/shadow/ShadowRoot.cpp

Index: Source/core/dom/shadow/ShadowRoot.cpp
diff --git a/Source/core/dom/shadow/ShadowRoot.cpp b/Source/core/dom/shadow/ShadowRoot.cpp
index 49e4db35bb203dd1fd425241a72772a62f2da6a9..74ec90c20ca3258f10b964e65e8f0e7e5c973692 100644
--- a/Source/core/dom/shadow/ShadowRoot.cpp
+++ b/Source/core/dom/shadow/ShadowRoot.cpp
@@ -316,10 +316,8 @@ const WillBeHeapVector<RefPtrWillBeMember<InsertionPoint> >& ShadowRoot::descend
         return emptyList;
 
     WillBeHeapVector<RefPtrWillBeMember<InsertionPoint> > insertionPoints;
-    for (Element* element = ElementTraversal::firstWithin(*this); element; element = ElementTraversal::next(*element, this)) {
-        if (element->isInsertionPoint())
-            insertionPoints.append(toInsertionPoint(element));
-    }
+    for (InsertionPoint* insertionPoint = Traversal<InsertionPoint>::firstWithin(*this); insertionPoint; insertionPoint = Traversal<InsertionPoint>::next(*insertionPoint, this))
+        insertionPoints.append(insertionPoint);
 
     ensureShadowRootRareData()->setDescendantInsertionPoints(insertionPoints);