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diff --git a/layout/painting/ActiveLayerTracker.h b/layout/painting/ActiveLayerTracker.h
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+++ b/layout/painting/ActiveLayerTracker.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 ACTIVELAYERTRACKER_H_
+#define ACTIVELAYERTRACKER_H_
+
+#include "nsCSSPropertyID.h"
+
+class nsIFrame;
+class nsIContent;
+class nsCSSPropertyIDSet;
+class nsDOMCSSDeclaration;
+
+namespace mozilla {
+
+class nsDisplayListBuilder;
+
+/**
+ * This class receives various notifications about style changes and content
+ * changes that affect layerization decisions, and implements the heuristics
+ * that drive those decisions. It manages per-frame state to support those
+ * heuristics.
+ */
+class ActiveLayerTracker {
+ public:
+  static void Shutdown();
+
+  /*
+   * We track style changes to selected styles:
+   *   eCSSProperty_transform, eCSSProperty_translate,
+   *   eCSSProperty_rotate, eCSSProperty_scale
+   *   eCSSProperty_offset_path, eCSSProperty_offset_distance,
+   *   eCSSProperty_offset_rotate, eCSSProperty_offset_anchor,
+   *   eCSSProperty_opacity
+   * and use that information to guess whether style changes are animated.
+   */
+
+  /**
+   * Notify aFrame's style property as having changed due to a restyle,
+   * and therefore possibly wanting an active layer to render that style.
+   * Any such marking will time out after a short period.
+   * @param aProperty the property that has changed
+   */
+  static void NotifyRestyle(nsIFrame* aFrame, nsCSSPropertyID aProperty);
+
+  /**
+   * Notify that a property in the inline style rule of aFrame's element
+   * has been modified.
+   */
+  static void NotifyInlineStyleRuleModified(nsIFrame* aFrame,
+                                            nsCSSPropertyID aProperty);
+  /**
+   * Notify that a frame needs to be repainted. This is important for layering
+   * decisions where, say, aFrame's transform is updated from JS, but we need
+   * to repaint aFrame anyway, so we get no benefit from giving it its own
+   * layer.
+   */
+  static void NotifyNeedsRepaint(nsIFrame* aFrame);
+  /**
+   * Return true if aFrame's property style in |aPropertySet| should be
+   * considered as being animated for constructing active layers.
+   */
+  static bool IsStyleAnimated(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
+                              const nsCSSPropertyIDSet& aPropertySet);
+  /**
+   * Return true if aFrame's transform-like property,
+   * i.e. transform/translate/rotate/scale, is animated.
+   */
+  static bool IsTransformAnimated(nsDisplayListBuilder* aBuilder,
+                                  nsIFrame* aFrame);
+  /**
+   * Return true if aFrame's transform style should be considered as being
+   * animated for pre-rendering.
+   */
+  static bool IsTransformMaybeAnimated(nsIFrame* aFrame);
+  /**
+   * Return true if aFrame either has an animated scale now, or is likely to
+   * have one in the future because it has a CSS animation or transition
+   * (which may not be playing right now) that affects its scale.
+   */
+  static bool IsScaleSubjectToAnimation(nsIFrame* aFrame);
+
+  /**
+   * Transfer the LayerActivity property to the frame's content node when the
+   * frame is about to be destroyed so that layer activity can be tracked
+   * throughout reframes of an element. Only call this when aFrame is the
+   * primary frame of aContent.
+   */
+  static void TransferActivityToContent(nsIFrame* aFrame, nsIContent* aContent);
+  /**
+   * Transfer the LayerActivity property back to the content node's primary
+   * frame after the frame has been created.
+   */
+  static void TransferActivityToFrame(nsIContent* aContent, nsIFrame* aFrame);
+};
+
+}  // namespace mozilla
+
+#endif /* ACTIVELAYERTRACKER_H_ */