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

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

 #!/usr/bin/env python
 
 import subprocess
 import sys
 
 import css_properties
 import in_generator
 import license
 
 
@@ skipping 212 matching lines @@
             'license': license.license_for_generated_cpp(),
             'class_name': self.class_name,
             'property_name_strings': '\n'.join('    "%s\\0"' % name for name in property_names),
             'property_name_offsets': '\n'.join('    %d,' % offset for offset in property_offsets),
             'property_to_enum_map': '\n'.join('%s, %s' % property for property in css_name_and_enum_pairs),
         }
         # 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__":
     in_generator.Maker(CSSPropertyNamesWriter).main(sys.argv)