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diff --git a/mfbt/RollingMean.h b/mfbt/RollingMean.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/. */
+
+/* A set abstraction for enumeration values. */
+
+#ifndef mozilla_RollingMean_h_
+#define mozilla_RollingMean_h_
+
+#include "mozilla/Assertions.h"
+#include "mozilla/TypeTraits.h"
+#include "mozilla/Vector.h"
+
+#include <stddef.h>
+
+namespace mozilla {
+
+/**
+ * RollingMean<T> calculates a rolling mean of the values it is given. It
+ * accumulates the total as values are added and removed. The second type
+ * argument S specifies the type of the total. This may need to be a bigger
+ * type in order to maintain that the sum of all values in the average doesn't
+ * exceed the maximum input value.
+ *
+ * WARNING: Float types are not supported due to rounding errors.
+ */
+template<typename T, typename S>
+class RollingMean
+{
+private:
+  size_t mInsertIndex;
+  size_t mMaxValues;
+  Vector<T> mValues;
+  S mTotal;
+
+public:
+  static_assert(!IsFloatingPoint<T>::value,
+                "floating-point types are unsupported due to rounding "
+                "errors");
+
+  explicit RollingMean(size_t aMaxValues)
+    : mInsertIndex(0),
+      mMaxValues(aMaxValues),
+      mTotal(0)
+  {
+    MOZ_ASSERT(aMaxValues > 0);
+  }
+
+  RollingMean& operator=(RollingMean&& aOther)
+  {
+    MOZ_ASSERT(this != &aOther, "self-assignment is forbidden");
+    this->~RollingMean();
+    new(this) RollingMean(aOther.mMaxValues);
+    mInsertIndex = aOther.mInsertIndex;
+    mTotal = aOther.mTotal;
+    mValues.swap(aOther.mValues);
+    return *this;
+  }
+
+  /**
+   * Insert a value into the rolling mean.
+   */
+  bool insert(T aValue)
+  {
+    MOZ_ASSERT(mValues.length() <= mMaxValues);
+
+    if (mValues.length() == mMaxValues) {
+      mTotal = mTotal - mValues[mInsertIndex] + aValue;
+      mValues[mInsertIndex] = aValue;
+    } else {
+      if (!mValues.append(aValue)) {
+        return false;
+      }
+      mTotal = mTotal + aValue;
+    }
+
+    mInsertIndex = (mInsertIndex + 1) % mMaxValues;
+    return true;
+  }
+
+  /**
+   * Calculate the rolling mean.
+   */
+  T mean()
+  {
+    MOZ_ASSERT(!empty());
+    return T(mTotal / int64_t(mValues.length()));
+  }
+
+  bool empty()
+  {
+    return mValues.empty();
+  }
+
+  /**
+   * Remove all values from the rolling mean.
+   */
+  void clear()
+  {
+    mValues.clear();
+    mInsertIndex = 0;
+    mTotal = T(0);
+  }
+
+  size_t maxValues()
+  {
+    return mMaxValues;
+  }
+};
+
+} // namespace mozilla
+
+#endif // mozilla_RollingMean_h_