Update from https://crrev.com/316786

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 47 matching lines @@
  *          PrimitiveType(DOMString)
  *      Error(Missing argument.)
  *    Type()
  *      PrimitiveType(void)
  */
 interface MyIFaceMissingArgument {
   void foo(DOMString arg, );
 };
 
 /* TREE
+ *Error(Unexpected keyword "double" after keyword "readonly".)
+ */
+interface MyIFaceMissingAttribute {
+  readonly double foo;
+};
+
+/* TREE
  *Interface(MyIFaceBig)
  *  Const(setString)
  *    PrimitiveType(DOMString)
  *    Value(NULL)
  */
 interface MyIFaceBig {
   const DOMString? setString = null;
 };
 
 /* TREE
@@ skipping 214 matching lines @@
  *    Type()
  *      PrimitiveType(long)
  *  Setlike()
  *    Type()
  *      PrimitiveType(double)
  */
 interface MyIfaceSetlike {
   readonly setlike<long>;
   setlike<double>;
 };