[Telemetry] Add a profiler based loading measurement.

tools/perf/measurements/loading_profile.py

+# Copyright (c) 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.
+
+import os
+import tempfile
+
+from telemetry.core import util
+from telemetry.core.platform.profiler import perf_profiler
+from telemetry.page import page_measurement
+
+class LoadingProfile(page_measurement.PageMeasurement):
+  def __init__(self):
+    super(LoadingProfile, self).__init__(discard_first_result=True)
+
+  @property
+  def results_are_the_same_on_every_page(self):
+    return False
+
+  def AddCommandLineOptions(self, parser):
+    # In order to change the default of an option, we must remove and re-add it.
+    page_repeat_option = parser.get_option('--page-repeat')
+    page_repeat_option.default = 2
+    parser.remove_option('--page-repeat')
+    parser.add_option(page_repeat_option)
+
+  def CustomizeBrowserOptions(self, options):
+    options.AppendExtraBrowserArg('--no-sandbox')
+
+  def WillNavigateToPage(self, page, tab):
+    tab.browser.StartProfiling(perf_profiler.PerfProfiler.name(),
+                               os.path.join(tempfile.mkdtemp(),
+                                            page.url_as_file_safe_name))
+
+  def MeasurePage(self, page, tab, results):
+    # In current telemetry tests, all tests wait for DocumentComplete state,
+    # but we need to wait for the load event.
+    def IsLoaded():
+      return bool(tab.EvaluateJavaScript('performance.timing.loadEventStart'))
+    util.WaitFor(IsLoaded, 300)
+
+    profile_files = tab.browser.StopProfiling()
+
+    load_timings = tab.EvaluateJavaScript('window.performance.timing')
+    load_time_ms = (
+      float(load_timings['loadEventStart']) -
+      load_timings['navigationStart'])
+    dom_content_loaded_time_ms = (
+      float(load_timings['domContentLoadedEventStart']) -
+      load_timings['navigationStart'])
+    results.Add('load_time', 'ms', load_time_ms)
+    results.Add('dom_content_loaded_time', 'ms',
+                dom_content_loaded_time_ms)
+
+    profile_file = None
+    for profile_file in profile_files:
+      if 'renderer' in profile_file:
+        break
+
+    for function, period in perf_profiler.PerfProfiler.GetTopSamples(
+        profile_file, 10).iteritems():
+      results.Add(function.replace('.', '_'), 'period', period)