Add keyword_subset field template and generate text-decoration-line.

third_party/WebKit/Source/build/scripts/make_css_value_id_mappings.py

 #!/usr/bin/env python
 # Copyright 2017 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.
 
 import json5_generator
 import template_expander
 import make_style_builder
 
 from name_utilities import enum_for_css_keyword, enum_value_name
 
 
 class CSSValueIDMappingsWriter(make_style_builder.StyleBuilderWriter):
     def __init__(self, json5_file_path):
         super(CSSValueIDMappingsWriter, self).__init__(json5_file_path)
         self._outputs = {
             'CSSValueIDMappingsGenerated.h': self.generate_css_value_mappings,
         }
 
     @template_expander.use_jinja('CSSValueIDMappingsGenerated.h.tmpl')
     def generate_css_value_mappings(self):
         mappings = {}
         include_paths = set()
         for property_ in self._properties.values():
-            if property_['field_template'] == 'keyword':
+            if property_['field_template'] in ('keyword', 'multi_keyword'):
                 include_paths.update(property_['include_paths'])
 
                 mappings[property_['type_name']] = {
                     'default_value': enum_value_name(property_['default_value']),
                     'mapping': [(enum_value_name(k), enum_for_css_keyword(k)) for k in property_['keywords']],
                 }
 
         return {
             'include_paths': list(sorted(include_paths)),
             'mappings': mappings,
         }
 
 if __name__ == '__main__':
     json5_generator.Maker(CSSValueIDMappingsWriter).main()