[css-typed-om] Remove DOMString from StylePropertyMap iterable values.

Author: shans

css-typed-om/Overview.bs

@@ -92,7 +92,7 @@ interface StylePropertyMapReadOnly {
 	CSSStyleValue? get(DOMString property);
 	sequence<CSSStyleValue> getAll(DOMString property);
 	boolean has(DOMString property);
-	iterable<DOMString, (CSSStyleValue or sequence<CSSStyleValue> or DOMString)>;
+	iterable<DOMString, (CSSStyleValue or sequence<CSSStyleValue>)>;
 	sequence<DOMString> getProperties();
 	stringifier;
 };