Update from https://crrev.com/328418

mojo/common/task_tracker.cc

 // Copyright 2015 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.
 
 #include "mojo/common/task_tracker.h"
 
 #include <vector>
 
 #include "base/location.h"
 #include "base/logging.h"
@@ skipping 36 matching lines @@
                                const void* program_counter) {
   // So far we don't track nested invocations.
   if (IsAlive())
     return false;
   birth_ = tracked_objects::ThreadData::TallyABirthIfActive(
       tracked_objects::Location(function_name, file_name, line_number,
                                 program_counter));
   if (!birth_)
     return false;
 
-  tracked_objects::ThreadData::PrepareForStartOfRun(birth_);
   (new (stopwatch()) tracked_objects::TaskStopwatch())->Start();
   return true;
 }
 
 void TrackingActivation::End() {
   DCHECK(IsAlive());
   stopwatch()->Stop();
   tracked_objects::ThreadData::TallyRunInAScopedRegionIfTracking(birth_,
                                                                  *stopwatch());
   stopwatch()->tracked_objects::TaskStopwatch::~TaskStopwatch();
@@ skipping 26 matching lines @@
 void TaskTracker::EndTracking(intptr_t id) {
   if (0 == id)
     return;
   // |EndTracking()| must be called from the same thread of |StartTracking()|.
   DCHECK_EQ(reinterpret_cast<TrackingActivation*>(id), g_activation.Get());
   reinterpret_cast<TrackingActivation*>(id)->End();
 }
 
 }  // namespace common
 }  // namespace mojo