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

tools/perf/benchmarks/media.py

Index: tools/perf/benchmarks/media.py
diff --git a/tools/perf/benchmarks/media.py b/tools/perf/benchmarks/media.py
index a45fd5d5bc90e4f8ac2772d26f4a38664ef95da0..e42f55cc62d13b7ea21bc6d4bde91d34bee0eef2 100644
--- a/tools/perf/benchmarks/media.py
+++ b/tools/perf/benchmarks/media.py
@@ -6,6 +6,7 @@ from measurements import media
 import page_sets
 from telemetry import benchmark
 from telemetry.page import page_test
+from telemetry.value import improvement_direction
 from telemetry.value import list_of_scalar_values
 from telemetry.value import scalar
 
@@ -25,12 +26,14 @@ class _MSEMeasurement(page_test.PageTest):
         results.AddValue(list_of_scalar_values.ListOfScalarValues(
                 results.current_page, trace_name, units='ms',
                 values=[float(v) for v in metrics[m]],
-                important=True))
+                important=True,
+                improvement_direction=improvement_direction.DOWN))
 
       else:
         results.AddValue(scalar.ScalarValue(
                 results.current_page, trace_name, units='ms',
-                value=float(metrics[m]), important=True))
+                value=float(metrics[m]), important=True,
+                improvement_direction=improvement_direction.DOWN))
 
 
 @benchmark.Disabled('android')