LayoutFullScreen::m_placeholder is LayoutBlockFlow.

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

 /*
  * Copyright (C) 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 36 matching lines @@
     void setStyle(PassRefPtr<ComputedStyle>) = delete;
 
 private:
     bool isOfType(LayoutObjectType type) const override { return type == LayoutObjectLayoutFullScreenPlaceholder || LayoutBlockFlow::isOfType(type); }
     void willBeDestroyed() override;
     LayoutFullScreen* m_owner;
 };
 
 void LayoutFullScreenPlaceholder::willBeDestroyed()
 {
-    m_owner->setPlaceholder(nullptr);
+    m_owner->resetPlaceholder();
     LayoutBlockFlow::willBeDestroyed();
 }
 
 LayoutFullScreen::LayoutFullScreen()
     : LayoutFlexibleBox(nullptr)
     , m_placeholder(nullptr)
 {
     setIsAtomicInlineLevel(false);
 }
 
@@ skipping 106 matching lines @@
             parent()->addChild(child, this);
             parent()->setNeedsLayoutAndPrefWidthsRecalcAndFullPaintInvalidation(LayoutInvalidationReason::Fullscreen);
         }
     }
     if (placeholder())
         placeholder()->remove();
     remove();
     destroy();
 }
 
-void LayoutFullScreen::setPlaceholder(LayoutBlock* placeholder)
-{
-    m_placeholder = placeholder;
-}
-
 void LayoutFullScreen::createPlaceholder(PassRefPtr<ComputedStyle> style, const LayoutRect& frameRect)
 {
     if (style->width().isAuto())
         style->setWidth(Length(frameRect.width(), Fixed));
     if (style->height().isAuto())
         style->setHeight(Length(frameRect.height(), Fixed));
 
     if (!m_placeholder) {
         m_placeholder = new LayoutFullScreenPlaceholder(this);
         m_placeholder->setStyleWithWritingModeOfParent(style);
         if (parent()) {
             parent()->addChildWithWritingModeOfParent(m_placeholder, this);
             parent()->setNeedsLayoutAndPrefWidthsRecalcAndFullPaintInvalidation(LayoutInvalidationReason::Fullscreen);
         }
     } else {
         m_placeholder->setStyle(style);
         m_placeholder->setStyleWithWritingModeOfParent(style);
     }
 }