webkit: Catch OSError for when gperf isn't avaliable.

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

 #!/usr/bin/env python
 
 import os.path
 import re
 import subprocess
 import sys
 
 from name_utilities import enum_for_css_keyword
 from name_utilities import upper_first_letter
 import json5_generator
@@ skipping 147 matching lines @@
             'value_keyword_strings': '\n'.join('    "%(name)s\\0"' % keyword for keyword in self._value_keywords),
             'value_keyword_offsets': '\n'.join('  %d,' % offset for offset in keyword_offsets),
             'value_keyword_to_enum_map': '\n'.join('%(lower_name)s, %(enum_name)s' % keyword for keyword in self._value_keywords),
             'ua_sheet_mode_values_keywords': '\n        '.join(map(self._case_value_keyword, self._value_keywords_with_mode('UASheet'))),
             '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 gperf isn't in the path we get an OSError. We don't want to use
+        # the normal solution of shell=True (as this has to run on many
+        # platforms), so instead we catch the error and raise a
+        # CalledProcessError like subprocess would do when shell=True is set.
+        try:
+            gperf = subprocess.Popen(gperf_args, stdin=subprocess.PIPE, stdout=subprocess.PIPE, universal_newlines=True)
+            return gperf.communicate(gperf_input)[0]
+        except OSError:
+            raise subprocess.CalledProcessError(127, gperf_args, output='Command not found.')
 
 
 if __name__ == "__main__":
     json5_generator.Maker(CSSValueKeywordsWriter).main()