[Telemetry] Add tracing_agent API.

tools/perf/measurements/smoothness_controller.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.
 import sys
 
 from measurements import smooth_gesture_util
 from telemetry.core.platform import tracing_category_filter
 from telemetry.core.platform import tracing_options
 from telemetry.timeline import trace_data as trace_data_module
 from telemetry.timeline.model import TimelineModel
@@ skipping 19 matching lines @@
   def SetUp(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']
     custom_categories += page.GetSyntheticDelayCategories()
     category_filter = tracing_category_filter.TracingCategoryFilter()
     for c in custom_categories:
       category_filter.AddIncludedCategory(c)
     options = tracing_options.TracingOptions()
     options.enable_chrome_trace = True
-    if tab.browser.platform.tracing_controller.IsDisplayTracingSupported():
-      options.enable_platform_display_trace = True
+    options.enable_platform_display_trace = True
     tab.browser.platform.tracing_controller.Start(options, category_filter, 60)
 
   def Start(self, tab):
     # Start the smooth marker for all smooth actions.
     runner = action_runner.ActionRunner(tab)
     self._interaction = runner.BeginInteraction(
         RUN_SMOOTH_ACTIONS, is_smooth=True)
 
   def Stop(self, tab):
     # End the smooth marker for  all smooth actions.
@@ skipping 42 matching lines @@
     # Create an interaction_record for this legacy measurement. Since we don't
     # wrap the results that are sent to smoothness metric, the label will
     # not be used.
     smoothness_metric = smoothness.SmoothnessMetric()
     smoothness_metric.AddResults(
         self._timeline_model, renderer_thread, smooth_records, results)
 
   def CleanUp(self, tab):
     if tab.browser.platform.tracing_controller.is_tracing_running:
       tab.browser.platform.tracing_controller.Stop()