telemetry: Make trace profiler work with trace-based benchmarks.

tools/perf/metrics/timeline.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.
 import collections
 
 from metrics import Metric
 
 TRACING_MODE = 'tracing-mode'
 TIMELINE_MODE = 'timeline-mode'
 
@@ skipping 20 matching lines @@
   def Stop(self, page, tab):
     if self._mode == TRACING_MODE:
       # This creates an async trace event in the render process for tab that
       # will allow us to find that tab during the AddTracingResultsForTab
       # function.
       tab.ExecuteJavaScript("""
           console.time("__loading_measurement_was_here__");
           console.timeEnd("__loading_measurement_was_here__");
           """)
 
-      tab.browser.StopTracing()
-      trace_result = tab.browser.GetTraceResultAndReset()
+      trace_result = tab.browser.StopTracing()
       self._model = trace_result.AsTimelineModel()
       events = [s for
                 s in self._model.GetAllEventsOfName(
                     '__loading_measurement_was_here__')
                 if s.parent_slice == None]
       assert len(events) == 1
       self._thread_for_tab = events[0].start_thread
     else:
       tab.StopTimelineRecording()
       self._model = tab.timeline_model
       self._thread_for_tab = self._model.GetAllThreads()[0]
 
   def AddResults(self, tab, results):
     assert self._model
 
     events = self._thread_for_tab.all_slices
 
     events_by_name = collections.defaultdict(list)
     for e in events:
       events_by_name[e.name].append(e)
 
     for event_name, event_group in events_by_name.iteritems():
       times = [event.self_time for event in event_group]
       total = sum(times)
       biggest_jank = max(times)
       results.Add(event_name, 'ms', total)
       results.Add(event_name + '_max', 'ms', biggest_jank)
       results.Add(event_name + '_avg', 'ms', total / len(times))
-