Extract AD policy scheduler into separate class

components/policy/core/common/policy_scheduler.cc

+// Copyright 2017 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/policy/core/common/policy_scheduler.h"
+
+#include "base/memory/ptr_util.h"
+#include "base/threading/thread_task_runner_handle.h"
+
+namespace policy {
+
+PolicyScheduler::PolicyScheduler(Task task,
+                                 SchedulerCallback callback,
+                                 base::TimeDelta interval,
+                                 base::TimeDelta backoff_interval)
+    : task_(task),
+      callback_(callback),
+      interval_(interval),
+      backoff_interval_(backoff_interval) {
+  ScheduleTask(base::TimeDelta());
+}
+
+PolicyScheduler::~PolicyScheduler() = default;
+
+void PolicyScheduler::ScheduleTask(base::TimeDelta delay) {

[pmarko, 2017/06/19 10:14:37]

Have you considered using SequenceChecker to make sure that member functions are
not called concurrently from different threads (especially ScheduleTask vs.
OnTaskDone)?

[Thiemo Nagel, 2017/06/19 22:29:51]

Good point.  I've added it to all methods to save myself and the readers from
having to reason whether a specific method could be called from outside the
class or not.

+  if (job_) {
+    job_->Cancel();
+  }
+  job_ = base::MakeUnique<base::CancelableClosure>(base::Bind(
+      &PolicyScheduler::RunScheduledTask, weak_ptr_factory_.GetWeakPtr()));
+  base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(FROM_HERE,
+                                                       job_->callback(), delay);
+}
+
+void PolicyScheduler::ScheduleNextTask() {
+  base::TimeTicks baseline;
+  base::TimeDelta interval;
+  if (backoff_) {
+    baseline = last_task_;
+    interval = backoff_interval_;
+  } else if (last_task_ == base::TimeTicks()) {

[pmarko, 2017/06/19 10:14:37]

Can this happen? ScheduleNextTask() is private and only called from
OnTaskDone(), which sets last_task_ before that.

[Thiemo Nagel, 2017/06/19 22:29:51]

Good catch! I think that part only made sense in the previous version of the
scheduler that contained an initial delay.

+    baseline = startup_;
+    interval = base::TimeDelta();
+  } else {
+    baseline = last_task_;
+    interval = interval_;
+  }
+  const base::TimeTicks now(base::TimeTicks::Now());
+  // Time uses saturated arithmetics thus no under/overflow possible.
+  const base::TimeDelta delay = baseline + interval - now;
+  // Clamping delay to non-negative values just to be on the safe side.
+  ScheduleTask(std::max(base::TimeDelta(), delay));
+}
+
+void PolicyScheduler::RunScheduledTask() {
+  if (task_in_progress_) {
+    backoff_ = true;
+    return;
+  }
+
+  backoff_ = false;
+  task_in_progress_ = true;
+  task_.Run(base::BindOnce(&PolicyScheduler::OnTaskDone,
+                           weak_ptr_factory_.GetWeakPtr()));
+}
+
+void PolicyScheduler::OnTaskDone(bool success) {
+  task_in_progress_ = false;
+  last_task_ = base::TimeTicks::Now();
+  callback_.Run(success);
+  ScheduleNextTask();
+}
+
+}  // namespace policy