Factor out a base class from RuntimeFeatureWriter

Source/core/core.gyp/core_derived_sources.gyp

 #
 # Copyright (C) 2013 Google Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
@@ skipping 135 matching lines @@
             '-o',
             '<@(_outputs)',
             '<@(_inputs)'
           ],
         },
         {
           'action_name': 'RuntimeEnabledFeatures',
           'inputs': [
             '../scripts/make_runtime_features.py',
             '../scripts/in_file.py',
+            '../scripts/in_generator.py',
             '../scripts/license.py',
             '../page/RuntimeEnabledFeatures.in',
           ],
           'outputs': [
             '<(SHARED_INTERMEDIATE_DIR)/webkit/RuntimeEnabledFeatures.cpp',
             '<(SHARED_INTERMEDIATE_DIR)/webkit/RuntimeEnabledFeatures.h',
           ],
           'action': [
             'python',
             '../scripts/make_runtime_features.py',
@@ skipping 464 matching lines @@
             '../scripts/make-hash-tools.pl',
             '<(SHARED_INTERMEDIATE_DIR)/webkit',
             '<(RULE_INPUT_PATH)',
             '<(gperf_exe)',
           ],
         },
       ],
     },
   ],
 }