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diff --git a/xpcom/threads/IdleTaskRunner.h b/xpcom/threads/IdleTaskRunner.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef IdleTaskRunner_h
+#define IdleTaskRunner_h
+
+#include "mozilla/TimeStamp.h"
+#include "nsIEventTarget.h"
+#include "nsISupports.h"
+#include "nsITimer.h"
+#include <functional>
+
+namespace mozilla {
+
+class IdleTaskRunnerTask;
+
+// A general purpose repeating callback runner (it can be configured to a
+// one-time runner, too.) If it is running repeatedly, one has to either
+// explicitly Cancel() the runner or have MayStopProcessing() callback return
+// true to completely remove the runner.
+class IdleTaskRunner {
+ public:
+  friend class IdleTaskRunnerTask;
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(IdleTaskRunner)
+
+  // Return true if some meaningful work was done.
+  using CallbackType = std::function<bool(TimeStamp aDeadline)>;
+
+  // A callback for "stop processing" decision. Return true to
+  // stop processing. This can be an alternative to Cancel() or
+  // work together in different way.
+  using MayStopProcessingCallbackType = std::function<bool()>;
+
+  // A callback to be invoked when an interrupt is requested
+  // (eg during an idle activity when the user presses a key.)
+  // The callback takes an "interrupt priority" value as its
+  // sole parameter.
+  using RequestInterruptCallbackType = std::function<void(uint32_t)>;
+
+ public:
+  // An IdleTaskRunner has (up to) three phases:
+  //
+  //  - (duration aStartDelay) waiting to run (aStartDelay can be zero)
+  //
+  //  - (duration aMaxDelay) attempting to find a long enough amount of idle
+  //    time, at least aMinimumUsefulBudget
+  //
+  //  - overdue for idle time, run as soon as possible
+  //
+  // If aRepeating is true, then aStartDelay applies only to the first run; the
+  // second run will attempt to run in the first idle slice that is long
+  // enough.
+  //
+  // All durations are in milliseconds.
+  //
+  static already_AddRefed<IdleTaskRunner> Create(
+      const CallbackType& aCallback, const char* aRunnableName,
+      TimeDuration aStartDelay, TimeDuration aMaxDelay,
+      TimeDuration aMinimumUsefulBudget, bool aRepeating,
+      const MayStopProcessingCallbackType& aMayStopProcessing,
+      const RequestInterruptCallbackType& aRequestInterrupt = nullptr);
+
+  void Run();
+
+  // (Used by the task triggering code.) Record the end of the current idle
+  // period, or null if not running during idle time.
+  void SetIdleDeadline(mozilla::TimeStamp aDeadline);
+
+  // If the timer is already active, SetTimer doesn't do anything.
+  void SetTimer(TimeDuration aDelay, nsIEventTarget* aTarget);
+
+  void ResetTimer(TimeDuration aDelay);
+
+  // Update the minimum idle time that this callback would be invoked for.
+  void SetMinimumUsefulBudget(int64_t aMinimumUsefulBudget);
+
+  void Cancel();
+
+  void Schedule(bool aAllowIdleDispatch);
+
+  const char* GetName() { return mName; }
+
+ private:
+  explicit IdleTaskRunner(
+      const CallbackType& aCallback, const char* aRunnableName,
+      TimeDuration aStartDelay, TimeDuration aMaxDelay,
+      TimeDuration aMinimumUsefulBudget, bool aRepeating,
+      const MayStopProcessingCallbackType& aMayStopProcessing,
+      const RequestInterruptCallbackType& aRequestInterrupt);
+  ~IdleTaskRunner();
+  void CancelTimer();
+  void SetTimerInternal(TimeDuration aDelay);
+
+  nsCOMPtr<nsITimer> mTimer;
+  nsCOMPtr<nsITimer> mScheduleTimer;
+  CallbackType mCallback;
+
+  // Do not run until this time.
+  const mozilla::TimeStamp mStartTime;
+
+  // Wait this long for idle time before giving up and running a non-idle
+  // callback.
+  TimeDuration mMaxDelay;
+
+  // If running during idle time, the expected end of the current idle period.
+  // The null timestamp when the run is triggered by aMaxDelay instead of idle.
+  TimeStamp mDeadline;
+
+  // The least duration worth calling the callback for during idle time.
+  TimeDuration mMinimumUsefulBudget;
+
+  bool mRepeating;
+  bool mTimerActive;
+  MayStopProcessingCallbackType mMayStopProcessing;
+  RequestInterruptCallbackType mRequestInterrupt;
+  const char* mName;
+  RefPtr<IdleTaskRunnerTask> mTask;
+};
+
+}  // end of namespace mozilla.
+
+#endif