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diff --git a/dom/base/nsStubMutationObserver.h b/dom/base/nsStubMutationObserver.h
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+++ b/dom/base/nsStubMutationObserver.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/. */
+
+/*
+ * nsStubMutationObserver is an implementation of the nsIMutationObserver
+ * interface (except for the methods on nsISupports) that is intended to be
+ * used as a base class within the content/layout library.  All methods do
+ * nothing.
+ */
+
+#ifndef nsStubMutationObserver_h_
+#define nsStubMutationObserver_h_
+
+#include "nsTHashMap.h"
+#include "nsIMutationObserver.h"
+
+/**
+ * There are two advantages to inheriting from nsStubMutationObserver
+ * rather than directly from nsIMutationObserver:
+ *  1. smaller compiled code size (since there's no need for the code
+ *     for the empty virtual function implementations for every
+ *     nsIMutationObserver implementation)
+ *  2. the performance of document's loop over observers benefits from
+ *     the fact that more of the functions called are the same (which
+ *     can reduce instruction cache misses and perhaps improve branch
+ *     prediction)
+ */
+class nsStubMutationObserver : public nsIMutationObserver {
+ public:
+  NS_DECL_NSIMUTATIONOBSERVER
+};
+
+class MutationObserverWrapper;
+
+/**
+ * @brief Base class for MutationObservers that are used by multiple nodes.
+ *
+ * Mutation Observers are stored inside of a nsINode using a DoublyLinkedList,
+ * restricting the number of nodes a mutation observer can be inserted to one.
+ *
+ * To allow a mutation observer to be used by several nodes, this class
+ * provides a MutationObserverWrapper which implements the nsIMutationObserver
+ * interface and forwards all method calls to this class. For each node this
+ * mutation observer will be used for, a wrapper object is created.
+ */
+class nsMultiMutationObserver : public nsIMutationObserver {
+ public:
+  /**
+   * Adds the mutation observer to aNode by creating a MutationObserverWrapper
+   * and inserting it into aNode.
+   * Does nothing if there already is a mutation observer for aNode.
+   */
+  void AddMutationObserverToNode(nsINode* aNode);
+
+  /**
+   * Removes the mutation observer from aNode.
+   * Does nothing if there is no mutation observer for aNode.
+   */
+  void RemoveMutationObserverFromNode(nsINode* aNode);
+
+  /**
+   * Returns true if there is already a mutation observer for aNode.
+   */
+  bool ContainsNode(const nsINode* aNode) const;
+
+ private:
+  friend class MutationObserverWrapper;
+  nsTHashMap<nsINode*, MutationObserverWrapper*> mWrapperForNode;
+};
+
+/**
+ * Convenience class that provides support for multiple nodes and has
+ * default implementations for nsIMutationObserver.
+ */
+class nsStubMultiMutationObserver : public nsMultiMutationObserver {
+ public:
+  NS_DECL_NSIMUTATIONOBSERVER
+};
+
+#endif /* !defined(nsStubMutationObserver_h_) */