LayoutBox (not LayoutBlock) is the common base for floats and out-of-flow objects.

third_party/WebKit/Source/core/layout/LayoutBox.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 223 matching lines @@
 
 void LayoutBox::styleDidChange(StyleDifference diff, const ComputedStyle* oldStyle)
 {
     // Horizontal writing mode definition is updated in LayoutBoxModelObject::updateFromStyle,
     // (as part of the LayoutBoxModelObject::styleDidChange call below). So, we can safely cache the horizontal
     // writing mode value before style change here.
     bool oldHorizontalWritingMode = isHorizontalWritingMode();
 
     LayoutBoxModelObject::styleDidChange(diff, oldStyle);
 
+    if (isFloatingOrOutOfFlowPositioned() && oldStyle && !oldStyle->isFloating() && !oldStyle->hasOutOfFlowPosition() && parent() && parent()->isLayoutBlockFlow())
+        toLayoutBlockFlow(parent())->childBecameFloatingOrOutOfFlow(this);
+
     const ComputedStyle& newStyle = styleRef();
     if (needsLayout() && oldStyle)
         removeFromPercentHeightContainer();
 
     if (oldHorizontalWritingMode != isHorizontalWritingMode()) {
         if (oldStyle) {
             if (isOrthogonalWritingModeRoot())
                 markOrthogonalWritingModeRoot();
             else
                 unmarkOrthogonalWritingModeRoot();
@@ skipping 4694 matching lines @@
         m_rareData->m_snapAreas->remove(&snapArea);
     }
 }
 
 SnapAreaSet* LayoutBox::snapAreas() const
 {
     return m_rareData ? m_rareData->m_snapAreas.get() : nullptr;
 }
 
 } // namespace blink