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diff --git a/dom/base/SimpleTreeIterator.h b/dom/base/SimpleTreeIterator.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/. */
+
+/**
+ * This is a light-weight tree iterator for `for` loops when full iterator
+ * functionality isn't required.
+ */
+
+#ifndef mozilla_dom_SimpleTreeIterator_h
+#define mozilla_dom_SimpleTreeIterator_h
+
+#include "nsINode.h"
+#include "nsTArray.h"
+#include "mozilla/dom/Element.h"
+
+namespace mozilla {
+namespace dom {
+
+class SimpleTreeIterator {
+public:
+  /**
+   * Initialize an iterator with aRoot. After that it can be iterated with a
+   * range-based for loop. At the moment, that's the only supported form of use
+   * for this iterator.
+   */
+  explicit SimpleTreeIterator(nsINode& aRoot)
+    : mCurrent(&aRoot)
+  {
+    mTree.AppendElement(&aRoot);
+  }
+
+  // Basic support for range-based for loops.
+  // This will modify the iterator as it goes.
+  SimpleTreeIterator& begin() { return *this; }
+
+  SimpleTreeIterator end() { return SimpleTreeIterator(); }
+
+  bool operator!=(const SimpleTreeIterator& aOther) {
+    return mCurrent != aOther.mCurrent;
+  }
+
+  void operator++() { Next(); }
+
+  nsINode* operator*() { return mCurrent; }
+
+private:
+  // Constructor used only for end() to represent a drained iterator.
+  SimpleTreeIterator()
+    : mCurrent(nullptr)
+  {}
+
+  void Next() {
+    MOZ_ASSERT(mCurrent, "Don't call Next() when we have no current node");
+
+    mCurrent = mCurrent->GetNextNode(mTree.LastElement());
+  }
+
+  // The current node.
+  nsINode* mCurrent;
+
+  // The DOM tree that we're inside of right now.
+  AutoTArray<nsINode*, 1> mTree;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_SimpleTreeIterator_h