Telemetry: Use mimimum tracing for timeline benchmarks.

tools/perf/measurements/thread_times.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.
 
 from metrics import timeline
 from telemetry.page import page_measurement
 
 class ThreadTimes(page_measurement.PageMeasurement):
   def __init__(self):
     super(ThreadTimes, self).__init__('smoothness')
     self._metric = None
 
   def AddCommandLineOptions(self, parser):
     parser.add_option('--report-silk-results', action='store_true',
                       help='Report results relevant to silk.')
     parser.add_option('--report-silk-details', action='store_true',
                       help='Report details relevant to silk.')
 
   def CanRunForPage(self, page):
     return hasattr(page, 'smoothness')
 
   @property
   def results_are_the_same_on_every_page(self):
     return False
 
   def WillRunActions(self, page, tab):
     self._metric = timeline.ThreadTimesTimelineMetric()
-    self._metric.Start(page, tab)
     if self.options.report_silk_results:
       self._metric.results_to_report = timeline.ReportSilkResults
     if self.options.report_silk_details:
       self._metric.details_to_report = timeline.ReportSilkDetails
+    self._metric.Start(page, tab)
 
   def DidRunAction(self, page, tab, action):
     self._metric.AddActionToIncludeInMetric(action)
 
   def DidRunActions(self, page, tab):
     self._metric.Stop(page, tab)
 
   def MeasurePage(self, page, tab, results):
     self._metric.AddResults(tab, results)