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 820fa374d75b903c481eccdddd2071a02df1874f..2d7752761d205e85c4cb9bc189dcdc8fb61945e0 100644
--- a/tools/perf/benchmarks/media.py
+++ b/tools/perf/benchmarks/media.py
@@ -21,12 +21,13 @@ 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, higher_is_better=False))
 
       else:
         results.AddValue(scalar.ScalarValue(
                 results.current_page, trace_name, units='ms',
-                value=float(metrics[m]), important=True))
+                value=float(metrics[m]), important=True,
+                higher_is_better=False))
 
 
 @benchmark.Disabled('android')