[Telemetry] Resolve errors due to new pylint checker.

tools/telemetry/telemetry/results/csv_pivot_table_output_formatter.py

 # Copyright 2014 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 csv
 
 from telemetry.results import output_formatter
 from telemetry.value import scalar
 
 
@@ skipping 17 matching lines @@
 
   def __init__(self, output_stream, trace_tag=''):
     super(CsvPivotTableOutputFormatter, self).__init__(output_stream)
     self._trace_tag = trace_tag
 
   def Format(self, page_test_results):
     csv_writer = csv.writer(self.output_stream)
 
     # Observe trace_tag. Use comma to split up the trace tag.
     tag_values = self._trace_tag.split(',')
-    tag_values = filter(lambda x: x, tag_values) # filter empty list entries
+    tag_values = [x for x in tag_values if x] # filter empty list entries
     tag_headers = ['trace_tag_%d' % i for i in range(len(tag_values))]
 
     # Write header.
     csv_writer.writerow(self.FIELDS + tag_headers)
 
     # Write all values. Each row contains a value + page-level metadata.
     for run in page_test_results.all_page_runs:
       run_index = page_test_results.all_page_runs.index(run)
       page_dict = {
           'page': run.page.display_name,
           'page_set': run.page.page_set.Name(),
           'run_index': run_index,
       }
       for value in run.values:
         if isinstance(value, scalar.ScalarValue):
           value_dict = {
             'name': value.name,
             'value': value.value,
             'units': value.units,
           }
           value_dict.update(page_dict.items())
           csv_writer.writerow(
               [value_dict[field] for field in self.FIELDS] + tag_values)