[telemetry] Implement first version of timeline based measurement

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()