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-rw-r--r--dom/base/nsStubMutationObserver.h35
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diff --git a/dom/base/nsStubMutationObserver.h 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 "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
+};
+
+#endif /* !defined(nsStubMutationObserver_h_) */