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diff --git a/gfx/src/TiledRegion.h b/gfx/src/TiledRegion.h
new file mode 100644
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+++ b/gfx/src/TiledRegion.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 MOZILLA_GFX_TILEDREGION_H_
+#define MOZILLA_GFX_TILEDREGION_H_
+
+#include <utility>
+
+#include "mozilla/ArrayView.h"
+#include "mozilla/gfx/Rect.h"
+#include "nsRegion.h"
+#include "pixman.h"
+
+namespace mozilla {
+namespace gfx {
+
+// See TiledRegion.cpp for documentation on TiledRegionImpl.
+class TiledRegionImpl {
+ public:
+  void Clear() { mRects.Clear(); }
+  bool AddRect(const pixman_box32_t& aRect);
+  bool Intersects(const pixman_box32_t& aRect) const;
+  bool Contains(const pixman_box32_t& aRect) const;
+  operator ArrayView<pixman_box32_t>() const {
+    return ArrayView<pixman_box32_t>(mRects);
+  }
+
+ private:
+  nsTArray<pixman_box32_t> mRects;
+};
+
+/**
+ * A auto-simplifying region type that supports one rectangle per tile.
+ * The virtual tile grid is anchored at (0, 0) and has quadratic tiles whose
+ * size is hard-coded as kTileSize in TiledRegion.cpp.
+ * A TiledRegion starts out empty. You can add rectangles or (regular) regions
+ * into it by calling Add(). Add() is a mutating union operation (similar to
+ * OrWith on nsRegion) that's *not* exact, because it will enlarge the region as
+ * necessary to satisfy the "one rectangle per tile" requirement.
+ * Tiled regions convert implicitly to the underlying regular region type.
+ * The only way to remove parts from a TiledRegion is by calling SetEmpty().
+ */
+template <typename RegionT>
+class TiledRegion {
+ public:
+  typedef typename RegionT::RectType RectT;
+
+  TiledRegion() : mCoversBounds(false) {}
+
+  TiledRegion(const TiledRegion& aOther)
+      : mBounds(aOther.mBounds), mImpl(aOther.mImpl), mCoversBounds(false) {}
+
+  TiledRegion(TiledRegion&& aOther)
+      : mBounds(aOther.mBounds),
+        mImpl(std::move(aOther.mImpl)),
+        mCoversBounds(false) {}
+
+  RegionT GetRegion() const {
+    if (mBounds.IsEmpty()) {
+      return RegionT();
+    }
+    if (mCoversBounds) {
+      // Rect limit hit or allocation failed, treat as 1 rect.
+      return RegionT(mBounds);
+    }
+    return RegionT(mImpl);
+  }
+
+  TiledRegion& operator=(const TiledRegion& aOther) {
+    if (&aOther != this) {
+      mBounds = aOther.mBounds;
+      mImpl = aOther.mImpl;
+      mCoversBounds = aOther.mCoversBounds;
+    }
+    return *this;
+  }
+
+  void Add(const RectT& aRect) {
+    if (aRect.IsEmpty()) {
+      return;
+    }
+
+    Maybe<RectT> newBounds = mBounds.SafeUnion(aRect);
+    if (!newBounds) {
+      return;
+    }
+    mBounds = newBounds.value();
+    MOZ_ASSERT(!mBounds.Overflows());
+
+    if (mCoversBounds) {
+      return;
+    }
+
+    if (!mImpl.AddRect(RectToBox(aRect))) {
+      FallBackToBounds();
+    }
+  }
+
+  void Add(const RegionT& aRegion) {
+    Maybe<RectT> newBounds = mBounds.SafeUnion(aRegion.GetBounds());
+    if (!newBounds) {
+      return;
+    }
+    mBounds = newBounds.value();
+    MOZ_ASSERT(!mBounds.Overflows());
+
+    if (mCoversBounds) {
+      return;
+    }
+
+    for (auto iter = aRegion.RectIter(); !iter.Done(); iter.Next()) {
+      RectT r = iter.Get();
+      if (r.IsEmpty() || r.Overflows()) {
+        // This can happen if e.g. a negative-width rect was wrapped into a
+        // region. Treat it the same as we would if such a rect was passed to
+        // the Add(const RectT&) function.
+        continue;
+      }
+      if (!mImpl.AddRect(RectToBox(r))) {
+        FallBackToBounds();
+        return;
+      }
+    }
+  }
+
+  bool IsEmpty() const { return mBounds.IsEmpty(); }
+
+  void SetEmpty() {
+    mBounds.SetEmpty();
+    mImpl.Clear();
+    mCoversBounds = false;
+  }
+
+  RectT GetBounds() const { return mBounds; }
+  bool CoversBounds() const { return mCoversBounds; }
+
+  bool Intersects(const RectT& aRect) const {
+    if (aRect.IsEmpty()) {
+      return true;
+    }
+    if (aRect.Overflows() || !mBounds.Intersects(aRect)) {
+      return false;
+    }
+    if (mCoversBounds) {
+      return true;
+    }
+
+    return mImpl.Intersects(RectToBox(aRect));
+  }
+
+  bool Contains(const RectT& aRect) const {
+    if (aRect.IsEmpty()) {
+      return true;
+    }
+    if (aRect.Overflows() || !mBounds.Contains(aRect)) {
+      return false;
+    }
+    if (mCoversBounds) {
+      return true;
+    }
+    return mImpl.Contains(RectToBox(aRect));
+  }
+
+ private:
+  void FallBackToBounds() {
+    mCoversBounds = true;
+    mImpl.Clear();
+  }
+
+  static pixman_box32_t RectToBox(const RectT& aRect) {
+    MOZ_ASSERT(!aRect.IsEmpty());
+    MOZ_ASSERT(!aRect.Overflows());
+    return {aRect.X(), aRect.Y(), aRect.XMost(), aRect.YMost()};
+  }
+
+  RectT mBounds;
+  TiledRegionImpl mImpl;
+
+  // mCoversBounds is true if we bailed out due to a large number of tiles.
+  // mCoversBounds being true means that this TiledRegion is just a simple
+  // rectangle (our mBounds).
+  // Once set to true, the TiledRegion will stay in this state until SetEmpty
+  // is called.
+  bool mCoversBounds;
+};
+
+typedef TiledRegion<IntRegion> TiledIntRegion;
+
+}  // namespace gfx
+}  // namespace mozilla
+
+#endif /* MOZILLA_GFX_TILEDREGION_H_ */