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diff --git a/gfx/layers/apz/util/ScrollLinkedEffectDetector.h b/gfx/layers/apz/util/ScrollLinkedEffectDetector.h
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+++ b/gfx/layers/apz/util/ScrollLinkedEffectDetector.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/. */
+
+#ifndef mozilla_layers_ScrollLinkedEffectDetector_h
+#define mozilla_layers_ScrollLinkedEffectDetector_h
+
+#include "mozilla/RefPtr.h"
+
+namespace mozilla {
+
+namespace dom {
+class Document;
+}
+
+namespace layers {
+
+// ScrollLinkedEffectDetector is used to detect the existence of a scroll-linked
+// effect on a webpage. Generally speaking, a scroll-linked effect is something
+// on the page that animates or changes with respect to the scroll position.
+// Content authors usually rely on running some JS in response to the scroll
+// event in order to implement such effects, and therefore it tends to be laggy
+// or work improperly with APZ enabled. This class helps us detect such an
+// effect so that we can warn the author and/or take other preventative
+// measures.
+class MOZ_STACK_CLASS ScrollLinkedEffectDetector final {
+ private:
+  static uint32_t sDepth;
+  static bool sFoundScrollLinkedEffect;
+
+ public:
+  static void PositioningPropertyMutated();
+
+  explicit ScrollLinkedEffectDetector(dom::Document*);
+  ~ScrollLinkedEffectDetector();
+
+ private:
+  RefPtr<dom::Document> mDocument;
+};
+
+}  // namespace layers
+}  // namespace mozilla
+
+#endif /* mozilla_layers_ScrollLinkedEffectDetector_h */