Fix "unreachable code" warnings (MSVC warning 4702) in Blink.

Source/build/scripts/make_css_value_keywords.py

 #!/usr/bin/env python
 
 import os.path
 import re
 import subprocess
 import sys
 
 from in_file import InFile
 import in_generator
 import license
@@ skipping 68 matching lines @@
 
 const char* getValueName(unsigned short id)
 {
     if (id >= numCSSValueKeywords || id <= 0)
         return 0;
     return valueListStringPool + valueListStringOffsets[id];
 }
 
 bool isValueAllowedInMode(unsigned short id, CSSParserMode mode)
 {
-    // FIXME: Investigate whether we can deprecate the former
-    // two as only QuirksOrUASheet is used in CSSValueKeyword.in
     switch (id) {
         %(ua_sheet_mode_values_keywords)s
             return isUASheetBehavior(mode);
-        %(quirks_mode_values_keywords)s
-            return isQuirksModeBehavior(mode);
         %(quirks_mode_or_ua_sheet_mode_values_keywords)s
             return isUASheetBehavior(mode) || isQuirksModeBehavior(mode);
         default:
             return true;
     }
 }
 
 } // namespace WebCore
 """
 
@@ skipping 51 matching lines @@
             keyword_offsets.append(current_offset)
             current_offset += len(keyword["name"]) + 1
 
         gperf_input = GPERF_TEMPLATE % {
             'license': license.license_for_generated_cpp(),
             'class_name': self.class_name,
             'value_keyword_strings': '\n'.join(map(lambda property: '    "%(name)s\\0"' % property, self._value_keywords)),
             'value_keyword_offsets': '\n'.join(map(lambda offset: '  %d,' % offset, keyword_offsets)),
             'value_keyword_to_enum_map': '\n'.join(map(lambda property: '%(name)s, %(enum_name)s' % property, self._value_keywords)),
             'ua_sheet_mode_values_keywords': '\n        '.join(map(self._case_value_keyword, self._value_keywords_with_mode('UASheet'))),
-            'quirks_mode_values_keywords': '\n        '.join(map(self._case_value_keyword, self._value_keywords_with_mode('Quirks'))),
             'quirks_mode_or_ua_sheet_mode_values_keywords': '\n    '.join(map(self._case_value_keyword, self._value_keywords_with_mode('QuirksOrUASheet'))),
         }
         # FIXME: If we could depend on Python 2.7, we would use subprocess.check_output
         gperf_args = [self.gperf_path, '--key-positions=*', '-P', '-n']
         gperf_args.extend(['-m', '50'])  # Pick best of 50 attempts.
         gperf_args.append('-D')  # Allow duplicate hashes -> More compact code.
         gperf = subprocess.Popen(gperf_args, stdin=subprocess.PIPE, stdout=subprocess.PIPE, universal_newlines=True)
         return gperf.communicate(gperf_input)[0]
 
 
 if __name__ == "__main__":
     in_generator.Maker(CSSValueKeywordsWriter).main(sys.argv)