IDL: Add error handlings to avoid infinite loops

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 32 matching lines @@
 
 /* TREE
  *Interface(MyIFacePartial)
  */
 partial interface MyIFacePartial { };
 
 /* ERROR Unexpected ":" after identifier "MyIFaceInherit". */
 partial interface MyIFaceInherit : Foo {};
 
 /* TREE
+ *Interface(MyIFaceMissingArgument)
+ *  Operation(foo)
+ *    Arguments()
+ *      Argument(arg)
+ *        Type()
+ *          PrimitiveType(DOMString)
+ *      Error(Missing argument.)
+ *    Type()
+ *      PrimitiveType(void)
+ */
+interface MyIFaceMissingArgument {
+  void foo(DOMString arg, );
+};
+
+/* TREE
  *Interface(MyIFaceBig)
  *  Const(setString)
  *    PrimitiveType(DOMString)
  *    Value(NULL)
  */
 interface MyIFaceBig {
   const DOMString? setString = null;
 };
 
 /* TREE
@@ skipping 145 matching lines @@
  *      Promise(Promise)
  *        Type()
  *          Any()
  */
 interface MyIfacePromise {
   Promise<void> method1();
   Promise<long> method2();
   Promise<any> method3();
   Promise method4();
 };