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

tools/perf/benchmarks/dom_perf.py

Index: tools/perf/benchmarks/dom_perf.py
diff --git a/tools/perf/benchmarks/dom_perf.py b/tools/perf/benchmarks/dom_perf.py
index af779b0f8d57b008bcdff478eb09797d95a183e8..440d1264299c539c094fdbb85346918b38021e84 100644
--- a/tools/perf/benchmarks/dom_perf.py
+++ b/tools/perf/benchmarks/dom_perf.py
@@ -51,7 +51,8 @@ class _DomPerfMeasurement(page_test.PageTest):
         if len(suite['Benchmarks']) or suite['score']:
           results.AddValue(scalar.ScalarValue(
               results.current_page, '%s.%s' % (suite['name'], SCORE_TRACE_NAME),
-              SCORE_UNIT, suite['score'], important=False))
+              SCORE_UNIT, suite['score'], important=False,
+              higher_is_better=True))

[tonyg, 2014/12/18 17:31:35]

For anything that is summarizable into a numeric value, I don't think we should
leave this parameter optional. There's no good way to check that we've
considered all of the cases in this CL and in the future, folks might forget to
specify.

That being said, we also don't want to have a naked boolean in the API. A couple
of ideas are:
- We could assert that the field is passed by name and continue to use a bool
- We could assert a different type besides bool that has a more readable name

     finally:
       tab.EvaluateJavaScript('document.cookie = "__domperf_finished=0"')