Implement autoplay gesture override experiment.

Source/core/layout/LayoutMedia.h

 /*
  * Copyright (C) 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 33 matching lines @@
     void slowFirstChild() const = delete;
     void slowLastChild() const = delete;
 
     const LayoutObjectChildList* children() const { return &m_children; }
     LayoutObjectChildList* children() { return &m_children; }
 
     HTMLMediaElement* mediaElement() const;
 
     const char* name() const override { return "LayoutMedia"; }
 
+    // Temporary callback for crbug.com/587345,402044
+    void notifyPositionMayHaveChanged();
+
+    // Change whether we want or don't want to receive position change
+    // notifications.  This will cause us to start / stop receiving change
+    // notifications if possible.
+    // Temporary method for crbug.com/587345,402044
+    void setRequestPositionUpdates(bool);
+
 protected:
+    // Temporary overrides for crbug.com/587345,402044
+    void willBeDestroyed() override;
+    void insertedIntoTree() override;
+    void willBeRemovedFromTree() override;
+
     void layout() override;
 
     bool isOfType(LayoutObjectType type) const override { return type == LayoutObjectMedia || LayoutImage::isOfType(type); }
 
 private:
     LayoutObjectChildList* virtualChildren() final { return children(); }
     const LayoutObjectChildList* virtualChildren() const final { return children(); }
 
     DeprecatedPaintLayerType layerTypeRequired() const override { return NormalDeprecatedPaintLayer; }
 
     bool canHaveChildren() const final { return true; }
     bool isChildAllowed(LayoutObject*, const ComputedStyle&) const final;
 
     bool isImage() const final { return false; }
     void paintReplaced(const PaintInfo&, const LayoutPoint&) override;
 
     bool backgroundShouldAlwaysBeClipped() const final { return false; }
 
+    // Register or unregister us for position change notifications, to match
+    // the argument.  Takes no action if not attached to a LayoutView or
+    // if we are already (un)registered correctly.
+    // Temporary helper for crbug.com/587345,402044
+    void updatePositionChangeRegistration(bool);
+
     LayoutObjectChildList m_children;
+
+    // Temporary state for crbug.com/587345,402044
+    bool m_registeredForPositionChangeNotifications;
+    bool m_wantPositionChangeNotifications;
 };
 
 DEFINE_LAYOUT_OBJECT_TYPE_CASTS(LayoutMedia, isMedia());
 
 } // namespace blink
 
 #endif // LayoutMedia_h