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diff --git a/accessible/base/EmbeddedObjCollector.h b/accessible/base/EmbeddedObjCollector.h
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+++ b/accessible/base/EmbeddedObjCollector.h
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+/* 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_EmbeddedObjCollector_h__
+#define mozilla_a11y_EmbeddedObjCollector_h__
+
+#include "nsTArray.h"
+
+namespace mozilla {
+namespace a11y {
+
+class LocalAccessible;
+
+/**
+ * Collect embedded objects. Provide quick access to accessible by index and
+ * vice versa.
+ */
+class EmbeddedObjCollector final {
+ public:
+  ~EmbeddedObjCollector() {}
+
+  /**
+   * Return index of the given accessible within the collection.
+   */
+  int32_t GetIndexAt(LocalAccessible* aAccessible);
+
+  /**
+   * Return accessible count within the collection.
+   */
+  uint32_t Count();
+
+  /**
+   * Return an accessible from the collection at the given index.
+   */
+  LocalAccessible* GetAccessibleAt(uint32_t aIndex);
+
+ protected:
+  /**
+   * Ensure accessible at the given index is stored and return it.
+   */
+  LocalAccessible* EnsureNGetObject(uint32_t aIndex);
+
+  /**
+   * Ensure index for the given accessible is stored and return it.
+   */
+  int32_t EnsureNGetIndex(LocalAccessible* aAccessible);
+
+  // Make sure it's used by LocalAccessible class only.
+  explicit EmbeddedObjCollector(LocalAccessible* aRoot)
+      : mRoot(aRoot), mRootChildIdx(0) {}
+
+  /**
+   * Append the object to collection.
+   */
+  void AppendObject(LocalAccessible* aAccessible);
+
+  friend class LocalAccessible;
+
+  LocalAccessible* mRoot;
+  uint32_t mRootChildIdx;
+  nsTArray<LocalAccessible*> mObjects;
+};
+
+}  // namespace a11y
+}  // namespace mozilla
+
+#endif