LibWeb: Added HTMLLinkElement.as

Author: https://github.com/Hexeption
Commit: 2f4668edce
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/39
Reviewed-by: https://github.com/AtkinsSJ
Reviewed-by: https://github.com/awesomekling
Reviewed-by: https://github.com/nico

Userland/Libraries/LibWeb/HTML/HTMLLinkElement.h

@@ -33,6 +33,8 @@ public:
     String rel() const { return get_attribute_value(HTML::AttributeNames::rel); }
     String type() const { return get_attribute_value(HTML::AttributeNames::type); }
     String href() const { return get_attribute_value(HTML::AttributeNames::href); }
+    String as() const;
+    WebIDL::ExceptionOr<void> set_as(String const&);
 
     JS::NonnullGCPtr<DOM::DOMTokenList> rel_list();