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

tools/telemetry/telemetry/web_perf/metrics/fast_metric.py

Index: tools/telemetry/telemetry/web_perf/metrics/fast_metric.py
diff --git a/tools/telemetry/telemetry/web_perf/metrics/fast_metric.py b/tools/telemetry/telemetry/web_perf/metrics/fast_metric.py
index 88b198918d969cc5f09a2e57c20c8f20f7b3816e..8b47595eab143bddc6b6e0e1fdb2325ac4fefb0f 100644
--- a/tools/telemetry/telemetry/web_perf/metrics/fast_metric.py
+++ b/tools/telemetry/telemetry/web_perf/metrics/fast_metric.py
@@ -5,6 +5,7 @@
 import logging
 
 from telemetry.timeline import bounds
+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 timeline_based_metric
@@ -53,7 +54,8 @@ class FastMetric(timeline_based_metric.TimelineBasedMetric):
 
     duration = sum(r.end - r.start for r in interaction_records)
     results.AddValue(scalar.ScalarValue(
-        results.current_page, 'fast-duration', 'ms', duration))
+        results.current_page, 'fast-duration', 'ms', duration,
+        improvement_direction=improvement_direction.DOWN))
 
     try:
       cpu_time = sum(
@@ -67,14 +69,16 @@ class FastMetric(timeline_based_metric.TimelineBasedMetric):
           repr(interaction_records))
     else:
       results.AddValue(scalar.ScalarValue(
-          results.current_page, 'fast-cpu_time', 'ms', cpu_time))
+          results.current_page, 'fast-cpu_time', 'ms', cpu_time,
+          improvement_direction=improvement_direction.DOWN))
 
     idle_time = duration - sum(
         bounds.Bounds.GetOverlap(r.start, r.end, s.start, s.end)
         for r in interaction_records
         for s in renderer_thread.toplevel_slices)
     results.AddValue(scalar.ScalarValue(
-        results.current_page, 'fast-idle_time', 'ms', idle_time))
+        results.current_page, 'fast-idle_time', 'ms', idle_time,
+        improvement_direction=improvement_direction.UP))
 
     v8_stats = v8_stats_module.V8Stats(renderer_thread, interaction_records)
 
@@ -82,20 +86,23 @@ class FastMetric(timeline_based_metric.TimelineBasedMetric):
       results.AddValue(scalar.ScalarValue(
           results.current_page, 'fast-' + event_stats.result_name, 'ms',
           event_stats.thread_duration,
-          event_stats.result_description))
+          event_stats.result_description,
+          improvement_direction=improvement_direction.DOWN))
       results.AddValue(scalar.ScalarValue(
           results.current_page,
           'fast-' + event_stats.result_name + '_outside_idle', 'ms',
           event_stats.thread_duration_outside_idle,
-          event_stats.result_description + 'outside of idle notifications'))
+          event_stats.result_description + 'outside of idle notifications',
+          improvement_direction=improvement_direction.DOWN))
 
     results.AddValue(scalar.ScalarValue(
         results.current_page, 'fast-total_garbage_collection', 'ms',
         v8_stats.total_gc_thread_duration,
-        'Total thread duration of all garbage collection events'))
+        'Total thread duration of all garbage collection events',
+        improvement_direction=improvement_direction.DOWN))
 
     results.AddValue(scalar.ScalarValue(
         results.current_page, 'fast-total_garbage_collection_outside_idle',
         'ms', v8_stats.total_gc_thread_duration_outside_idle,
         'Total thread duration of all garbage collection events outside of idle'
-        'notifications'))
+        'notifications', improvement_direction=improvement_direction.DOWN))