scheduler: Move the Blink scheduler into Blink

components/scheduler/base/queueing_time_estimator.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 "components/scheduler/base/queueing_time_estimator.h"
-
-#include "base/time/default_tick_clock.h"
-
-namespace scheduler {
-
-namespace {
-
-// This method computes the expected queueing time of a randomly distributed
-// task R within a window containing a single task T. Let T' be the time range
-// for which T overlaps the window. We first compute the probability that R will
-// start within T'. We then compute the expected queueing duration if R does
-// start within this range. Since the start time of R is uniformly distributed
-// within the window, this is equal to the average of the queueing times if R
-// started at the beginning or end of T'. The expected queueing time of T is the
-// probability that R will start within T', multiplied by the expected queueing
-// duration if R does fall in this range.
-base::TimeDelta ExpectedQueueingTimeFromTask(base::TimeTicks task_start,
-                                             base::TimeTicks task_end,
-                                             base::TimeTicks window_start,
-                                             base::TimeTicks window_end) {
-  DCHECK(task_start <= task_end);
-  DCHECK(task_start <= window_end);
-  DCHECK(window_start < window_end);
-  DCHECK(task_end >= window_start);
-  base::TimeTicks task_in_window_start_time =
-      std::max(task_start, window_start);
-  base::TimeTicks task_in_window_end_time =
-      std::min(task_end, window_end);
-  DCHECK(task_in_window_end_time <= task_in_window_end_time);
-
-  double probability_of_this_task =
-      static_cast<double>((task_in_window_end_time - task_in_window_start_time)
-                              .InMicroseconds()) /
-      (window_end - window_start).InMicroseconds();
-
-  base::TimeDelta expected_queueing_duration_within_task =
-      ((task_end - task_in_window_start_time) +
-       (task_end - task_in_window_end_time)) /
-      2;
-
-  return base::TimeDelta::FromMillisecondsD(
-      probability_of_this_task *
-      expected_queueing_duration_within_task.InMillisecondsF());
-}
-
-}  // namespace
-
-QueueingTimeEstimator::QueueingTimeEstimator(
-    QueueingTimeEstimator::Client* client,
-    base::TimeDelta window_duration)
-    : client_(client),
-      window_duration_(window_duration),
-      window_start_time_() {}
-
-void QueueingTimeEstimator::OnToplevelTaskCompleted(
-    base::TimeTicks task_start_time,
-    base::TimeTicks task_end_time) {
-  if (window_start_time_.is_null())
-    window_start_time_ = task_start_time;
-
-  while (TimePastWindowEnd(task_end_time)) {
-    if (!TimePastWindowEnd(task_start_time)) {
-      // Include the current task in this window.
-      current_expected_queueing_time_ += ExpectedQueueingTimeFromTask(
-          task_start_time, task_end_time, window_start_time_,
-          window_start_time_ + window_duration_);
-    }
-    client_->OnQueueingTimeForWindowEstimated(current_expected_queueing_time_);
-    window_start_time_ += window_duration_;
-    current_expected_queueing_time_ = base::TimeDelta();
-  }
-
-  current_expected_queueing_time_ += ExpectedQueueingTimeFromTask(
-      task_start_time, task_end_time, window_start_time_,
-      window_start_time_ + window_duration_);
-}
-
-bool QueueingTimeEstimator::TimePastWindowEnd(base::TimeTicks time) {
-  return time > window_start_time_ + window_duration_;
-}
-
-}  // namespace scheduler