Use stricter typing for NodeLists throughout the code base

Source/core/html/LabelableElement.h

Index: Source/core/html/LabelableElement.h
diff --git a/Source/core/html/LabelableElement.h b/Source/core/html/LabelableElement.h
index 59b3ccf4efe407720ed969972b081153423e4594..b633b8ab5a58a8128c85eb97c7f301800ae0df54 100644
--- a/Source/core/html/LabelableElement.h
+++ b/Source/core/html/LabelableElement.h
@@ -35,12 +35,14 @@
 
 namespace WebCore {
 
+class LabelsNodeList;
+
 // LabelableElement represents "labelable element" defined in the HTML
 // specification, and provides the implementation of the "labels" attribute.
 class LabelableElement : public HTMLElement {
 public:
     virtual ~LabelableElement();
-    PassRefPtrWillBeRawPtr<NodeList> labels();
+    PassRefPtrWillBeRawPtr<LabelsNodeList> labels();
     virtual bool supportLabels() const { return false; }
 
     virtual void trace(Visitor*) OVERRIDE;