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

tools/perf/benchmarks/maps.py

Index: tools/perf/benchmarks/maps.py
diff --git a/tools/perf/benchmarks/maps.py b/tools/perf/benchmarks/maps.py
index 85f8053e8e91bcb3f55570683eabc1235142070b..00678c076b0d2a1ddb1eedcbeaee7a79d8d5eb5e 100644
--- a/tools/perf/benchmarks/maps.py
+++ b/tools/perf/benchmarks/maps.py
@@ -24,9 +24,11 @@ class _MapsMeasurement(page_test.PageTest):
     total = re.search('total=([0-9]+)', test_results).group(1)
     render = re.search('render=([0-9.]+),([0-9.]+)', test_results).group(2)
     results.AddValue(scalar.ScalarValue(
-        results.current_page, 'total_time', 'ms', total))
+        results.current_page, 'total_time', 'ms', total,
+        higher_is_better=False))
     results.AddValue(scalar.ScalarValue(
-        results.current_page, 'render_mean_time', 'ms', render))
+        results.current_page, 'render_mean_time', 'ms', render,
+        higher_is_better=False))
 
 class MapsPage(page_module.Page):
   def __init__(self, page_set, base_dir):