[scheduler] Disable background thread load tracker by default.

third_party/WebKit/Source/platform/scheduler/base/thread_load_tracker.cc

 // Copyright 2016 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 "platform/scheduler/base/thread_load_tracker.h"
 
 #include <algorithm>
 
 namespace blink {
 namespace scheduler {
 
 ThreadLoadTracker::ThreadLoadTracker(base::TimeTicks now,
                                      const Callback& callback,
                                      base::TimeDelta reporting_interval,
                                      base::TimeDelta waiting_period)
     : time_(now),
-      thread_state_(ThreadState::ACTIVE),
+      thread_state_(ThreadState::PAUSED),
       last_state_change_time_(now),
       waiting_period_(waiting_period),
       reporting_interval_(reporting_interval),
       callback_(callback) {
   next_reporting_time_ = now + waiting_period_;
 }
 
 ThreadLoadTracker::~ThreadLoadTracker() {}
 
 void ThreadLoadTracker::Pause(base::TimeTicks now) {
@@ skipping 87 matching lines @@
   }
 }
 
 double ThreadLoadTracker::Load() {
   return run_time_inside_window_.InSecondsF() /
          reporting_interval_.InSecondsF();
 }
 
 }  // namespace scheduler
 }  // namespace blink