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

tools/perf/metrics/webrtc_stats.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 json
 import logging
 import re
 
 from metrics import Metric
 from telemetry.core import camel_case
+from telemetry.value import improvement_direction
 from telemetry.value import list_of_scalar_values
 
 INTERESTING_METRICS = {
     'packetsReceived': {
         'units': 'packets',
         'description': 'Packets received by the peer connection',
+        'improvement_direction': improvement_direction.DOWN,
     },
     'packetsSent': {
         'units': 'packets',
         'description': 'Packets sent by the peer connection',
+        'improvement_direction': improvement_direction.DOWN,
     },
     'googDecodeMs': {
         'units': 'ms',
         'description': 'Time spent decoding.',
+        'improvement_direction': improvement_direction.DOWN,
     },
     'googMaxDecodeMs': {
         'units': 'ms',
         'description': 'Maximum time spent decoding one frame.',
+        'improvement_direction': improvement_direction.DOWN,
     },
     # TODO(phoglund): Add much more interesting metrics.
 }
 
 
 def GetReportKind(report):
   if 'audioInputLevel' in report or 'audioOutputLevel' in report:
     return 'audio'
   if 'googFrameRateSent' in report or 'googFrameRateReceived' in report:
     return 'video'
@@ skipping 52 matching lines @@
       time_series = SortStatsIntoTimeSeries(report)
 
       for stat_name, values in time_series.iteritems():
         stat_name_underscored = camel_case.ToUnderscore(stat_name)
         trace_name = 'peer_connection_%d_%s' % (i, stat_name_underscored)
         general_name = StripAudioVideoDistinction(stat_name)
         results.AddValue(list_of_scalar_values.ListOfScalarValues(
             results.current_page, trace_name,
             INTERESTING_METRICS[general_name]['units'], values,
             description=INTERESTING_METRICS[general_name]['description'],
-            important=False))
+            important=False,
+            improvement_direction=INTERESTING_METRICS[
+                general_name]['improvement_direction']))