[tools/perf] Explicitly enable display tracing for smoothness metric

tools/perf/measurements/smoothness.py

 # 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_test
 from telemetry.timeline import tracing_category_filter
 from telemetry.web_perf import timeline_based_measurement
 from telemetry.web_perf.metrics import smoothness
 
 
@@ skipping 32 matching lines @@
 
   def WillNavigateToPage(self, page, tab):
     # FIXME: Remove webkit.console when blink.console lands in chromium and
     # the ref builds are updated. crbug.com/386847
     custom_categories = [
         'webkit.console', 'blink.console', 'benchmark', 'trace_event_overhead']
     category_filter = tracing_category_filter.TracingCategoryFilter(
         ','.join(custom_categories))
 
     options = timeline_based_measurement.Options(category_filter)
+    options.config.enable_platform_display_trace = True
     options.SetLegacyTimelineBasedMetrics([smoothness.SmoothnessMetric()])
     for delay in page.GetSyntheticDelayCategories():
       options.category_filter.AddSyntheticDelay(delay)
     self._tbm = timeline_based_measurement.TimelineBasedMeasurement(
         options, self._results_wrapper)
     self._tbm.WillRunStory(tab.browser.platform)
 
   def ValidateAndMeasurePage(self, _, tab, results):
     self._tbm.Measure(tab.browser.platform, results)
 
@@ skipping 10 matching lines @@
         '--enable-threaded-compositing',
         '--enable-gpu-benchmarking'
     ])
 
 
 class SmoothnessWithRestart(Smoothness):
 
   def __init__(self):
     super(SmoothnessWithRestart, self).__init__(
         needs_browser_restart_after_each_page=True)