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

tools/perf/measurements/record_per_area.py

Index: tools/perf/measurements/record_per_area.py
diff --git a/tools/perf/measurements/record_per_area.py b/tools/perf/measurements/record_per_area.py
index 3de7c7079b42d38a5d0d6866c727bcaffb4a20f7..a832338704889e579ad0dda48df0d2c456841bb0 100644
--- a/tools/perf/measurements/record_per_area.py
+++ b/tools/perf/measurements/record_per_area.py
@@ -6,6 +6,7 @@ import time
 
 from measurements import smoothness
 from telemetry.page import page_test
+from telemetry.value import improvement_direction
 from telemetry.value import scalar
 
 
@@ -56,4 +57,4 @@ class RecordPerArea(page_test.PageTest):
 
       results.AddValue(scalar.ScalarValue(
           results.current_page, 'area_%07d_%dx%d' % (area, width, height),
-          'ms', time_ms))
+          'ms', time_ms, improvement_direction=improvement_direction.DOWN))