PPAPI: Make generator support "no_interface_string"

ppapi/generators/test_cgen/interface.idl

 /*
  * Copyright (c) 2011 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.
  */
 
 /**
  * This file will test that the IDL snippet matches the comment.
  */
 
@@ skipping 23 matching lines @@
   int32_t mem4([in] blob_t ptr);
   int32_t mem5([out] blob_t ptr);
   [version=2.0] int32_t mem6([inout] blob_t ptr);
 };
 
 interface ifaceBar {
   int8_t testIface([in] ifaceFoo foo, [in] int32_t y);
   ifaceFoo createIface([in] str_t name);
 };
 
+[no_interface_string]
+interface ifaceNoString {
+  void mem();
+};
+
 struct struct2 {
   ifaceBar bar;
 };