IDL parser: align with current Web IDL specification

tools/idl_parser/test_parser/enum_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 Enum productions
 
 Run with --test to generate an AST and verify that all comments accurately
 reflect the state of the Nodes.
 
 BUILD Type(Name)
@@ skipping 49 matching lines @@
 */
 enum MealType2 {
   /* BUILD EnumItem(rice) */
   "rice",
   /* BUILD EnumItem(noodles) */
   "noodles",
   /* BUILD EnumItem(other) */
   "other"
 };
 
+/* TREE
+ *Enum(TrailingComma)
+ *  EnumItem(rice)
+ *  EnumItem(noodles)
+ *  EnumItem(other)
+*/
+enum TrailingComma {
+  "rice",
+  "noodles",
+  "other",
+};
+
 /* BUILD Error(Unexpected string "noodles" after string "rice".) */
 /* ERROR Unexpected string "noodles" after string "rice". */
 enum MissingComma {
   "rice"
   "noodles",
   "other"
 };
 
-/* BUILD Error(Trailing comma in block.) */
-/* ERROR Trailing comma in block. */
-enum TrailingComma {
-  "rice",
-  "noodles",
-  "other",
-};
-
 /* BUILD Error(Unexpected "," after ",".) */
 /* ERROR Unexpected "," after ",". */
 enum ExtraComma {
   "rice",
   "noodles",
   ,"other",
 };
 
 /* BUILD Error(Unexpected keyword "interface" after "{".) */
 /* ERROR Unexpected keyword "interface" after "{". */
@@ skipping 14 matching lines @@
 /* BUILD Enum(MealType3) */
 enum MealType3 {
   /* BUILD EnumItem(rice) */
   "rice",
   /* BUILD EnumItem(noodles) */
   "noodles",
   /* BUILD EnumItem(other) */
   "other"
 };