IDL parser: implement Stringifier production

tools/idl_parser/test_parser/interface_web.idl

 /* Copyright (c) 2013 The Chromium Authors. All rights reserved.
    Use of this source code is governed by a BSD-style license that can be
   found in the LICENSE file. */
 
 /* Test Interface productions
 
 Run with --test to generate an AST and verify that all comments accurately
 reflect the state of the Nodes.
 
 BUILD Type(Name)
@@ skipping 107 matching lines @@
  *    Arguments()
  *      Argument(arg)
  *        Type()
  *          Typeref(SomeType)
  */
 interface MyIFaceSpecials {
   setter creator void set(DOMString property);
   getter double (DOMString property);
   long long [5][6] GetFiveSix(SomeType arg);
 };
+
+/* TREE
+ *Interface(MyIFaceStringifiers)
+ *  Stringifier()
+ *  Stringifier()
+ *    Operation(_unnamed_)
+ *      Type()
+ *        PrimitiveType(DOMString)
+ *      Arguments()
+ *  Stringifier()
+ *    Operation(namedStringifier)
+ *      Type()
+ *        PrimitiveType(DOMString)
+ *      Arguments()
+ *  Stringifier()
+ *    Attribute(stringValue)
+ *      Type()
+ *        PrimitiveType(DOMString)
+ */
+interface MyIFaceStringifiers {
+  stringifier;
+  stringifier DOMString ();
+  stringifier DOMString namedStringifier();
+  stringifier attribute DOMString stringValue;
+};