Consistently use ElementTraversal API when looking for an Element

Source/core/html/HTMLAppletElement.cpp

Index: Source/core/html/HTMLAppletElement.cpp
diff --git a/Source/core/html/HTMLAppletElement.cpp b/Source/core/html/HTMLAppletElement.cpp
index 242e2ea2110e5537abe551532a048fd9f68d970b..1e87f4b0277ef8d77127aaaa805fa02ff3e39006 100644
--- a/Source/core/html/HTMLAppletElement.cpp
+++ b/Source/core/html/HTMLAppletElement.cpp
@@ -172,7 +172,7 @@ void HTMLAppletElement::updateWidgetInternal()
         paramValues.append(mayScript.string());
     }
 
-    for (Node* child = firstChild(); child; child = child->nextSibling()) {
+    for (Element* child = ElementTraversal::firstWithin(*this); child; child = ElementTraversal::nextSibling(*child)) {
         if (!child->hasTagName(paramTag))
             continue;