Introduce isHTMLLabelElement and toHTMLLabelElement

Source/core/html/HTMLLabelElement.h

Index: Source/core/html/HTMLLabelElement.h
diff --git a/Source/core/html/HTMLLabelElement.h b/Source/core/html/HTMLLabelElement.h
index 4e239ed2f9c2d9ab47fa4af4ae055be262ce690e..4c11115218a98206c8ba0f6308560295af9854ad 100644
--- a/Source/core/html/HTMLLabelElement.h
+++ b/Source/core/html/HTMLLabelElement.h
@@ -55,6 +55,22 @@ private:
     virtual void focus(bool restorePreviousSelection, FocusDirection) OVERRIDE;
 };
 
+inline bool isHTMLLabelElement(const Node* node)
+{
+    return node->hasTagName(HTMLNames::labelTag);
+}
+
+inline bool isHTMLLabelElement(const Element* element)
+{
+    return element->hasTagName(HTMLNames::labelTag);
+}
+
+inline HTMLLabelElement* toHTMLLabelElement(Node* node)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!node || isHTMLLabelElement(node));
+    return static_cast<HTMLLabelElement*>(node);
+}
+
 } //namespace
 
 #endif