Use stricter typing for NodeLists throughout the code base

Source/core/html/HTMLFormElement.cpp

Index: Source/core/html/HTMLFormElement.cpp
diff --git a/Source/core/html/HTMLFormElement.cpp b/Source/core/html/HTMLFormElement.cpp
index 5eac9c275addcc64eb77887090d8ddd800340e5f..6d0584c5ddfc87f394a74fb414a5d939d4ccf3bb 100644
--- a/Source/core/html/HTMLFormElement.cpp
+++ b/Source/core/html/HTMLFormElement.cpp
@@ -43,6 +43,7 @@
 #include "core/frame/csp/ContentSecurityPolicy.h"
 #include "core/html/HTMLCollection.h"
 #include "core/html/HTMLDialogElement.h"
+#include "core/html/HTMLFormControlsCollection.h"
 #include "core/html/HTMLImageElement.h"
 #include "core/html/HTMLInputElement.h"
 #include "core/html/HTMLObjectElement.h"
@@ -559,9 +560,9 @@ void HTMLFormElement::didAssociateByParser()
     UseCounter::count(document(), UseCounter::FormAssociationByParser);
 }
 
-PassRefPtrWillBeRawPtr<HTMLCollection> HTMLFormElement::elements()
+PassRefPtrWillBeRawPtr<HTMLFormControlsCollection> HTMLFormElement::elements()
 {
-    return ensureCachedHTMLCollection(FormControls);
+    return toHTMLFormControlsCollection(ensureCachedHTMLCollection(FormControls).get());
 }
 
 void HTMLFormElement::collectAssociatedElements(Node& root, FormAssociatedElement::List& elements) const