Add optional schema compiler error messages

tools/json_schema_compiler/test/json_schema_compiler_tests.gyp

 # Copyright (c) 2012 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.
 
 {
   'targets': [
     {
       'target_name': 'json_schema_compiler_tests',
       'type': 'static_library',
       'variables': {
         'chromium_code': 1,
         'schema_files': [
           'additional_properties.json',
           'any.json',
           'arrays.json',
           'callbacks.json',
           'choices.json',
           'crossref.json',
           'enums.json',
           'functions_as_parameters.json',
           'functions_on_types.json',
           'idl_basics.idl',
           'idl_object_types.idl',
           'objects.json',
           'simple_api.json',
+          'error_generation.json'
         ],
         'cc_dir': 'tools/json_schema_compiler/test',
         'root_namespace': 'test::api',
       },
       'inputs': [
         '<@(schema_files)',
       ],
       'sources': [
         '<@(schema_files)',
         'test_util.cc',
         'test_util.h',
       ],
       'includes': ['../../../build/json_schema_compile.gypi'],
       # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
       'msvs_disabled_warnings': [4267, ],
     },
   ],
 }