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

tools/perf/metrics/startup_metric.py

 # Copyright 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 import collections
 import json
 import logging
 
 from metrics import Metric
 
 from telemetry.core import util
 from telemetry.value import histogram_util
+from telemetry.value import improvement_direction
 from telemetry.value import scalar
 
 
 class StartupMetric(Metric):
   "A metric for browser startup time."
 
   HISTOGRAMS_TO_RECORD = {
     'messageloop_start_time' :
         'Startup.BrowserMessageLoopStartTimeFromMainEntry',
     'window_display_time' : 'Startup.BrowserWindowDisplay',
@@ skipping 64 matching lines @@
     # this, to get the same measures on all platform, we only measure the
     # foreground tab on all platforms.
 
     RecordTabLoadTime(tab.browser.foreground_tab)
 
     foreground_tab_stats = tab_load_times[0]
     foreground_tab_load_complete = ((foreground_tab_stats.load_start_ms +
         foreground_tab_stats.load_duration_ms) - browser_main_entry_time_ms)
     results.AddValue(scalar.ScalarValue(
         results.current_page, 'foreground_tab_load_complete', 'ms',
-        foreground_tab_load_complete))
+        foreground_tab_load_complete,
+        improvement_direction=improvement_direction.DOWN))
     if (foreground_tab_stats.request_start_ms > 0):
       results.AddValue(scalar.ScalarValue(
           results.current_page, 'foreground_tab_request_start', 'ms',
-          foreground_tab_stats.request_start_ms - browser_main_entry_time_ms))
+          foreground_tab_stats.request_start_ms - browser_main_entry_time_ms,
+          improvement_direction=improvement_direction.DOWN))
 
   def AddResults(self, tab, results):
     get_histogram_js = 'statsCollectionController.getBrowserHistogram("%s")'
 
     for display_name, histogram_name in self.HISTOGRAMS_TO_RECORD.iteritems():
       result = tab.EvaluateJavaScript(get_histogram_js % histogram_name)
       result = json.loads(result)
       measured_time = 0
 
       if 'sum' in result:
         # For all the histograms logged here, there's a single entry so sum
         # is the exact value for that entry.
         measured_time = result['sum']
       elif 'buckets' in result:
         measured_time = \
             (result['buckets'][0]['high'] + result['buckets'][0]['low']) / 2
 
       results.AddValue(scalar.ScalarValue(
-          results.current_page, display_name, 'ms', measured_time))
+          results.current_page, display_name, 'ms', measured_time,
+          improvement_direction=improvement_direction.DOWN))
 
     # Get tab load times.
     browser_main_entry_time_ms = self._GetBrowserMainEntryTime(tab)
     if (browser_main_entry_time_ms is None):
       print "Outdated Chrome version, browser main entry time not supported."
       return
     self._RecordTabLoadTimes(tab, browser_main_entry_time_ms, results)