IDL parser: implement Stringifier production

tools/idl_parser/test_parser/interface_web.idl

Index: tools/idl_parser/test_parser/interface_web.idl
diff --git a/tools/idl_parser/test_parser/interface_web.idl b/tools/idl_parser/test_parser/interface_web.idl
index accbf35ec928e2f4653fde023c95730c28018760..da1dfcdaace07ca6c4a544c8aac9dacdb89d74c8 100644
--- a/tools/idl_parser/test_parser/interface_web.idl
+++ b/tools/idl_parser/test_parser/interface_web.idl
@@ -137,3 +137,28 @@ interface MyIFaceSpecials {
   getter double (DOMString property);
   long long [5][6] GetFiveSix(SomeType arg);
 };
+
+/* TREE
+ *Interface(MyIFaceStringifiers)
+ *  Stringifier()
+ *  Stringifier()
+ *    Operation(_unnamed_)
+ *      Arguments()
+ *      Type()
+ *        PrimitiveType(DOMString)
+ *  Stringifier()
+ *    Operation(namedStringifier)
+ *      Arguments()
+ *      Type()
+ *        PrimitiveType(DOMString)
+ *  Stringifier()
+ *    Attribute(stringValue)
+ *      Type()
+ *        PrimitiveType(DOMString)
+ */
+interface MyIFaceStringifiers {
+  stringifier;
+  stringifier DOMString ();
+  stringifier DOMString namedStringifier();
+  stringifier attribute DOMString stringValue;
+};