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

tools/perf/metrics/webrtc_stats.py

Index: tools/perf/metrics/webrtc_stats.py
diff --git a/tools/perf/metrics/webrtc_stats.py b/tools/perf/metrics/webrtc_stats.py
index 4a787dd1afa16d87a8e5a9cda6d7a0cb689ad6ec..74d7bdd683b71463bf34661bb031d1f717650da4 100644
--- a/tools/perf/metrics/webrtc_stats.py
+++ b/tools/perf/metrics/webrtc_stats.py
@@ -14,18 +14,22 @@ INTERESTING_METRICS = {
     'packetsReceived': {
         'units': 'packets',
         'description': 'Packets received by the peer connection',
+        'higher_is_better': False,
     },
     'packetsSent': {
         'units': 'packets',
         'description': 'Packets sent by the peer connection',
+        'higher_is_better': False,
     },
     'googDecodeMs': {
         'units': 'ms',
         'description': 'Time spent decoding.',
+        'higher_is_better': False,
     },
     'googMaxDecodeMs': {
         'units': 'ms',
         'description': 'Maximum time spent decoding one frame.',
+        'higher_is_better': False,
     },
     # TODO(phoglund): Add much more interesting metrics.
 }
@@ -98,4 +102,5 @@ class WebRtcStatisticsMetric(Metric):
             results.current_page, trace_name,
             INTERESTING_METRICS[general_name]['units'], values,
             description=INTERESTING_METRICS[general_name]['description'],
-            important=False))
+            important=False, higher_is_better=INTERESTING_METRICS[
+                general_name]['higher_is_better']))