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

tools/perf/measurements/page_cycler.py

Index: tools/perf/measurements/page_cycler.py
diff --git a/tools/perf/measurements/page_cycler.py b/tools/perf/measurements/page_cycler.py
index 61991b0d87bf136c6fa05403a9ef6d0115c820cc..f5d017f1d940d9e7cfbf7fd7f8840b3718617e3b 100644
--- a/tools/perf/measurements/page_cycler.py
+++ b/tools/perf/measurements/page_cycler.py
@@ -125,7 +125,8 @@ class PageCycler(page_test.PageTest):
                     'time of a layout after the window.load event. Cold times '
                     'are the times when the page is loaded cold, i.e. without '
                     'loading it before, and warm times are times when the '
-                    'page is loaded after being loaded previously.'))
+                    'page is loaded after being loaded previously.',
+        higher_is_better=False))
 
     self._has_loaded_page[page.url] += 1