Add a simple NavigateMeasurement to measure time taken in navigate_steps

This is useful for pages (such as chromestatus.com) where the 'load' event
is not a good signal for 'page ready', but where there's some other condition,
easily expressible in navigate_steps, of that readiness.

R=dtu@chromium.org

Review URL: https://codereview.chromium.org/108303010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241888 0039d316-1c4b-4281-b951-d872f2087c98

tools/perf/measurements/navigate.py

@@ -0,0 +1,23 @@
+# Copyright 2013 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.page import page_measurement
+
+class NavigateMeasurement(page_measurement.PageMeasurement):
+  """ Measures time between navigation start and the end of the navigate_steps
+
+  For pages where the 'load' event isn't a good measurement point, this
+  measurement allows a page_set to have its loading sequence listed by
+  way of navigate_steps, with a navigation_time result measured
+  by performance.now().
+  """
+  def __init__(self):
+    super(NavigateMeasurement, self).__init__()
+    self._navigate_time = None
+
+  def DidNavigateToPage(self, page, tab):
+    self._navigate_time = int(tab.EvaluateJavaScript('performance.now()'))
+
+  def MeasurePage(self, page, tab, results):
+    results.Add('navigate_time', 'ms', self._navigate_time)