Convert smoothness to the new timeline based metric API.

tools/perf/metrics/timeline_based_metric.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.
 
+
 class TimelineBasedMetric(object):
   def __init__(self):
     """Computes metrics from a telemetry.core.timeline Model and a range
 
     """
     super(TimelineBasedMetric, self).__init__()
 
   def AddResults(self, model, renderer_thread,
                  interaction_record, results):
     """Computes and adds metrics for the interaction_record's time range.
 
     The override of this method should compute results on the data **only**
     within the interaction_record's start and end time.
 
     model is an instance of telemetry.core.timeline.model.TimelineModel.
     interaction_record is an instance of TimelineInteractionRecord.
     results is an instance of page.PageTestResults.
 
     """
     raise NotImplementedError()