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

tools/perf/measurements/task_execution_time.py

 # Copyright 2014 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.
 
 from telemetry.core.platform import tracing_category_filter
 from telemetry.core.platform import tracing_options
 from telemetry.timeline.model import TimelineModel
 from telemetry.page import page_test
 from telemetry.util import statistics
 from telemetry.value import scalar
@@ skipping 38 matching lines @@
 
     sorted_tasks = sorted(tasks,
       key=lambda slice: slice.median_self_duration, reverse=True)
 
     for task in sorted_tasks[:self.GetExpectedResultCount()]:
       results.AddValue(scalar.ScalarValue(
         results.current_page,
         task.key,
         'ms',
         task.median_self_duration,
-        description = 'Slowest tasks'))
+        description = 'Slowest tasks',
+        higher_is_better=False))
 
   @staticmethod
   def GetTasks(process):
     task_dictionary = {}
     depth = 1
     for parent, task_slice in enumerate(
           process.IterAllSlicesOfName('MessageLoop::RunTask')):
       ProcessTasksForSlice(task_dictionary, task_slice, depth, parent)
     # Return dictionary flattened into a list
     return task_dictionary.values()
@@ skipping 47 matching lines @@
   if key in dictionary:
     dictionary[key].Update(
         self_duration, total_duration, depth, parent)
   else:
     dictionary[key] = SliceData(
         key, self_duration, total_duration, depth, parent)
 
   # Process sub slices recursively
   for sub_slice in task_slice.sub_slices:
     ProcessTasksForSlice(dictionary, sub_slice, depth + 1, parent)