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..8fce0b6dd272d5f59012679c5c3654d67d159f20 100644
--- a/tools/perf/measurements/page_cycler.py
+++ b/tools/perf/measurements/page_cycler.py
@@ -25,6 +25,7 @@ from metrics import speedindex
 from metrics import v8_object_stats
 from telemetry.core import util
 from telemetry.page import page_test
+from telemetry.value import improvement_direction
 from telemetry.value import scalar
 
 
@@ -125,7 +126,8 @@ 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.',
+        improvement_direction=improvement_direction.DOWN))
 
     self._has_loaded_page[page.url] += 1