Added support for improvement_direction to relevant values, which is propogated to chartjson.

tools/telemetry/telemetry/web_perf/metrics/responsiveness_metric.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 logging
 
+from telemetry.value import improvement_direction
 from telemetry.value import scalar
 from telemetry.web_perf import timeline_interaction_record as tir_module
 from telemetry.web_perf.metrics import mainthread_jank_stats
 from telemetry.web_perf.metrics import timeline_based_metric
 
 
 class ResponsivenessMetric(timeline_based_metric.TimelineBasedMetric):
   """Computes metrics that measure respsonsiveness on the record ranges.
 
       total_big_jank_thread_time is the total thread duration of all top
@@ skipping 21 matching lines @@
     except tir_module.NoThreadTimeDataException as e:
       #TODO(nednguyen): Report the warning with page_results system.
       logging.warning(
           'Main thread jank metrics cannot be computed for records %s since '
           'trace does not contain thread time data. %s',
           repr(interaction_records), repr(e))
       return
 
     results.AddValue(scalar.ScalarValue(
         results.current_page, 'responsive-total_big_jank_thread_time', 'ms',
-        jank_stats.total_big_jank_thread_time))
+        jank_stats.total_big_jank_thread_time,
+        improvement_direction=improvement_direction.DOWN))
     results.AddValue(scalar.ScalarValue(
         results.current_page, 'responsive-biggest_jank_thread_time', 'ms',
-        jank_stats.biggest_jank_thread_time))
+        jank_stats.biggest_jank_thread_time,
+        improvement_direction=improvement_direction.DOWN))