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

tools/perf/metrics/loading.py

Index: tools/perf/metrics/loading.py
diff --git a/tools/perf/metrics/loading.py b/tools/perf/metrics/loading.py
index a05e073a7f9179b3f2797cf155dd427048c2d4f5..05bc6087786a495d2ee08e1369fbb3bfb5a696bc 100644
--- a/tools/perf/metrics/loading.py
+++ b/tools/perf/metrics/loading.py
@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 
 from metrics import Metric
+from telemetry.value import improvement_direction
 from telemetry.value import scalar
 
 class LoadingMetric(Metric):
@@ -21,26 +22,28 @@ class LoadingMetric(Metric):
     load_start = (
       float(load_timings['loadEventStart']) - load_timings['navigationStart'])
     results.AddValue(scalar.ScalarValue(
-        results.current_page, 'load_start', 'ms', load_start))
+        results.current_page, 'load_start', 'ms', load_start,
+        improvement_direction=improvement_direction.DOWN))
 
     dom_content_loaded_start = (
       float(load_timings['domContentLoadedEventStart']) -
       load_timings['navigationStart'])
     results.AddValue(scalar.ScalarValue(
         results.current_page, 'dom_content_loaded_start', 'ms',
-        dom_content_loaded_start))
+        dom_content_loaded_start,
+        improvement_direction=improvement_direction.DOWN))
 
     fetch_start = (
         float(load_timings['fetchStart']) - load_timings['navigationStart'])
     results.AddValue(scalar.ScalarValue(
         results.current_page, 'fetch_start', 'ms', fetch_start,
-        important=False))
+        important=False, improvement_direction=improvement_direction.DOWN))
 
     request_start = (
         float(load_timings['requestStart']) - load_timings['navigationStart'])
     results.AddValue(scalar.ScalarValue(
         results.current_page, 'request_start', 'ms', request_start,
-        important=False))
+        important=False, improvement_direction=improvement_direction.DOWN))
 
     # Phase measurements in milliseconds.
     domain_lookup_duration = (
@@ -48,22 +51,23 @@ class LoadingMetric(Metric):
         load_timings['domainLookupStart'])
     results.AddValue(scalar.ScalarValue(
         results.current_page, 'domain_lookup_duration', 'ms',
-        domain_lookup_duration, important=False))
+        domain_lookup_duration, important=False,
+        improvement_direction=improvement_direction.DOWN))
 
     connect_duration = (
         float(load_timings['connectEnd']) - load_timings['connectStart'])
     results.AddValue(scalar.ScalarValue(
         results.current_page, 'connect_duration', 'ms', connect_duration,
-        important=False))
+        important=False, improvement_direction=improvement_direction.DOWN))
 
     request_duration = (
         float(load_timings['responseStart']) - load_timings['requestStart'])
     results.AddValue(scalar.ScalarValue(
         results.current_page, 'request_duration', 'ms', request_duration,
-        important=False))
+        important=False, improvement_direction=improvement_direction.DOWN))
 
     response_duration = (
         float(load_timings['responseEnd']) - load_timings['responseStart'])
     results.AddValue(scalar.ScalarValue(
         results.current_page, 'response_duration', 'ms', response_duration,
-        important=False))
+        important=False, improvement_direction=improvement_direction.DOWN))