[telemetry] Implement first version of timeline based measurement

tools/perf/metrics/timeline_based_metric.py

Index: tools/perf/metrics/timeline_based_metric.py
diff --git a/tools/perf/metrics/timeline_based_metric.py b/tools/perf/metrics/timeline_based_metric.py
new file mode 100644
index 0000000000000000000000000000000000000000..6d9a8a2659b89c07200e26b2a50b8ec7e16ca34e
--- /dev/null
+++ b/tools/perf/metrics/timeline_based_metric.py
@@ -0,0 +1,19 @@
+# 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):
+    super(TimelineBasedMetric, self).__init__()
+
+  def AddResults(self, model, renderer_thread,
+                 metric_request, results, detailed_mode=False):
+    """ Override to actually add metrics to the results. Metric that overrides
+    this method should only compute metric on the data between time_bound.
+
+    model is a model of timeline APIT. (TODO: make a shared timeline superclass)
+    time_bound is an instance of telemetry.core.timeline.Bounds
+    results_prefix is the name of the interval to be displayed in results.
+    results is an instance of page.PageTestResults.
+    """
+    raise NotImplementedError()