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diff --git a/js/public/SliceBudget.h b/js/public/SliceBudget.h
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+++ b/js/public/SliceBudget.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 js_SliceBudget_h
+#define js_SliceBudget_h
+
+#include "mozilla/TimeStamp.h"
+
+#include <stdint.h>
+
+#include "jstypes.h"
+
+namespace js {
+
+struct JS_PUBLIC_API TimeBudget {
+  int64_t budget;
+
+  explicit TimeBudget(int64_t milliseconds) { budget = milliseconds; }
+};
+
+struct JS_PUBLIC_API WorkBudget {
+  int64_t budget;
+
+  explicit WorkBudget(int64_t work) { budget = work; }
+};
+
+/*
+ * This class records how much work has been done in a given collection slice,
+ * so that we can return before pausing for too long. Some slices are allowed
+ * to run for unlimited time, and others are bounded. To reduce the number of
+ * gettimeofday calls, we only check the time every 1000 operations.
+ */
+class JS_PUBLIC_API SliceBudget {
+  static mozilla::TimeStamp unlimitedDeadline;
+  static const intptr_t unlimitedStartCounter = INTPTR_MAX;
+
+  bool checkOverBudget();
+
+  SliceBudget();
+
+ public:
+  // Memory of the originally requested budget. If isUnlimited, neither of
+  // these are in use. If deadline==0, then workBudget is valid. Otherwise
+  // timeBudget is valid.
+  TimeBudget timeBudget;
+  WorkBudget workBudget;
+
+  mozilla::TimeStamp deadline;
+  intptr_t counter;
+
+  static const intptr_t CounterReset = 1000;
+
+  static const int64_t UnlimitedTimeBudget = -1;
+  static const int64_t UnlimitedWorkBudget = -1;
+
+  /* Use to create an unlimited budget. */
+  static SliceBudget unlimited() { return SliceBudget(); }
+
+  /* Instantiate as SliceBudget(TimeBudget(n)). */
+  explicit SliceBudget(TimeBudget time);
+
+  /* Instantiate as SliceBudget(WorkBudget(n)). */
+  explicit SliceBudget(WorkBudget work);
+
+  explicit SliceBudget(mozilla::TimeDuration time)
+      : SliceBudget(TimeBudget(time.ToMilliseconds())) {}
+
+  void makeUnlimited() {
+    MOZ_ASSERT(unlimitedDeadline);
+    deadline = unlimitedDeadline;
+    counter = unlimitedStartCounter;
+  }
+
+  void step(intptr_t amt = 1) { counter -= amt; }
+
+  bool isOverBudget() {
+    if (counter > 0) {
+      return false;
+    }
+    return checkOverBudget();
+  }
+
+  bool isWorkBudget() const { return deadline.IsNull(); }
+  bool isTimeBudget() const { return !deadline.IsNull() && !isUnlimited(); }
+  bool isUnlimited() const { return deadline == unlimitedDeadline; }
+
+  int describe(char* buffer, size_t maxlen) const;
+
+  static void Init();
+};
+
+}  // namespace js
+
+#endif /* js_SliceBudget_h */