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diff --git a/accessible/base/AccessibleOrProxy.h b/accessible/base/AccessibleOrProxy.h
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+++ b/accessible/base/AccessibleOrProxy.h
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+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=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_a11y_AccessibleOrProxy_h
+#define mozilla_a11y_AccessibleOrProxy_h
+
+#include "mozilla/a11y/Accessible.h"
+#include "mozilla/a11y/ProxyAccessible.h"
+#include "mozilla/a11y/Role.h"
+
+#include <stdint.h>
+
+namespace mozilla {
+namespace a11y {
+
+/**
+ * This class stores an Accessible* or a ProxyAccessible* in a safe manner
+ * with size sizeof(void*).
+ */
+class AccessibleOrProxy {
+ public:
+  MOZ_IMPLICIT AccessibleOrProxy(Accessible* aAcc)
+      : mBits(reinterpret_cast<uintptr_t>(aAcc)) {}
+  MOZ_IMPLICIT AccessibleOrProxy(ProxyAccessible* aProxy)
+      : mBits(aProxy ? (reinterpret_cast<uintptr_t>(aProxy) | IS_PROXY) : 0) {}
+  MOZ_IMPLICIT AccessibleOrProxy(decltype(nullptr)) : mBits(0) {}
+  MOZ_IMPLICIT AccessibleOrProxy() : mBits(0) {}
+
+  bool IsProxy() const { return mBits & IS_PROXY; }
+  ProxyAccessible* AsProxy() const {
+    if (IsProxy()) {
+      return reinterpret_cast<ProxyAccessible*>(mBits & ~IS_PROXY);
+    }
+
+    return nullptr;
+  }
+
+  bool IsAccessible() const { return !IsProxy(); }
+  Accessible* AsAccessible() const {
+    if (IsAccessible()) {
+      return reinterpret_cast<Accessible*>(mBits);
+    }
+
+    return nullptr;
+  }
+
+  bool IsNull() const { return mBits == 0; }
+
+  uint32_t ChildCount() const {
+    if (IsProxy()) {
+      return AsProxy()->ChildrenCount();
+    }
+
+    if (RemoteChildDoc()) {
+      return 1;
+    }
+
+    return AsAccessible()->ChildCount();
+  }
+
+  /**
+   * Return true if the object has children, false otherwise
+   */
+  bool HasChildren() const { return ChildCount() > 0; }
+
+  /**
+   * Return the child object either an accessible or a proxied accessible at
+   * the given index.
+   */
+  AccessibleOrProxy ChildAt(uint32_t aIdx) const {
+    if (IsProxy()) {
+      return AsProxy()->ChildAt(aIdx);
+    }
+
+    ProxyAccessible* childDoc = RemoteChildDoc();
+    if (childDoc && aIdx == 0) {
+      return childDoc;
+    }
+
+    return AsAccessible()->GetChildAt(aIdx);
+  }
+
+  /**
+   * Return the first child object.
+   */
+  AccessibleOrProxy FirstChild() {
+    if (IsProxy()) {
+      return AsProxy()->FirstChild();
+    }
+
+    ProxyAccessible* childDoc = RemoteChildDoc();
+    if (childDoc) {
+      return childDoc;
+    }
+
+    return AsAccessible()->FirstChild();
+  }
+
+  /**
+   * Return the last child object.
+   */
+  AccessibleOrProxy LastChild() {
+    if (IsProxy()) {
+      return AsProxy()->LastChild();
+    }
+
+    ProxyAccessible* childDoc = RemoteChildDoc();
+    if (childDoc) {
+      return childDoc;
+    }
+
+    return AsAccessible()->LastChild();
+  }
+
+  /**
+   * Return the next sibling object.
+   */
+  AccessibleOrProxy NextSibling() {
+    if (IsProxy()) {
+      return AsProxy()->NextSibling();
+    }
+
+    return AsAccessible()->NextSibling();
+  }
+
+  /**
+   * Return the prev sibling object.
+   */
+  AccessibleOrProxy PrevSibling() {
+    if (IsProxy()) {
+      return AsProxy()->PrevSibling();
+    }
+
+    return AsAccessible()->PrevSibling();
+  }
+
+  role Role() const {
+    if (IsProxy()) {
+      return AsProxy()->Role();
+    }
+
+    return AsAccessible()->Role();
+  }
+
+  int32_t IndexInParent() const;
+
+  AccessibleOrProxy Parent() const;
+
+  AccessibleOrProxy ChildAtPoint(int32_t aX, int32_t aY,
+                                 Accessible::EWhichChildAtPoint aWhichChild);
+
+  bool operator!=(const AccessibleOrProxy& aOther) const {
+    return mBits != aOther.mBits;
+  }
+
+  bool operator==(const AccessibleOrProxy& aOther) const {
+    return mBits == aOther.mBits;
+  }
+
+  // XXX these are implementation details that ideally would not be exposed.
+  uintptr_t Bits() const { return mBits; }
+  void SetBits(uintptr_t aBits) { mBits = aBits; }
+
+ private:
+  /**
+   * If this is an OuterDocAccessible, return the remote child document.
+   */
+  ProxyAccessible* RemoteChildDoc() const;
+
+  uintptr_t mBits;
+  static const uintptr_t IS_PROXY = 0x1;
+};
+
+}  // namespace a11y
+}  // namespace mozilla
+
+#endif