1# Copyright 2013 The Chromium Authors. All rights reserved.
2# Use of this source code is governed by a BSD-style license that can be
3# found in the LICENSE file.
4
5class Metric(object):
6  """Base class for all the metrics that are used by telemetry measurements.
7
8  The Metric class represents a way of measuring something. Metrics are
9  helper classes used by PageTests. Each PageTest may use
10  multiple metrics; each metric should be focussed on collecting data
11  about one thing.
12  """
13
14  @classmethod
15  def CustomizeBrowserOptions(cls, options):
16    """Add browser options that are required by this metric.
17
18    Some metrics do not have any special browser options that need
19    to be added, and they do not need to override this method; by
20    default, no browser options are added.
21
22    To add options here, call options.AppendExtraBrowserArgs(arg).
23    """
24    pass
25
26  def Start(self, page, tab):
27    """Start collecting data for this metric."""
28    pass
29
30  def Stop(self, page, tab):
31    """Stop collecting data for this metric (if applicable)."""
32    pass
33
34  def AddResults(self, tab, results):
35    """Add the data collected into the results object for a measurement.
36
37    Metrics may implement AddResults to provide a common way to add results
38    to the PageTestResults in PageTest.ValidateOrMeasurePage --
39    results should be added with results.AddValue(...).
40    """
41    raise NotImplementedError()
42