Reland of Don't change layout size due to top control show/hide

third_party/WebKit/Source/core/frame/FrameView.h

 /*
    Copyright (C) 1997 Martin Jones (mjones@kde.org)
              (C) 1998 Waldo Bastian (bastian@kde.org)
              (C) 1998, 1999 Torben Weis (weis@kde.org)
              (C) 1999 Lars Knoll (knoll@kde.org)
              (C) 1999 Antti Koivisto (koivisto@kde.org)
    Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. 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 566 matching lines @@
 
     void setScrollTranslation(PassRefPtr<TransformPaintPropertyNode> scrollTranslation) { m_scrollTranslation = scrollTranslation; }
     const TransformPaintPropertyNode* scrollTranslation() const { return m_scrollTranslation.get(); }
 
     void setContentClip(PassRefPtr<ClipPaintPropertyNode> contentClip) { m_contentClip = contentClip; }
     const ClipPaintPropertyNode* contentClip() const { return m_contentClip.get(); }
 
     // TODO(ojan): Merge this with IntersectionObserver once it lands.
     IntRect computeVisibleArea();
 
+    // Viewport size that should be used for viewport units (i.e. 'vh'/'vw').
+    FloatSize viewportSizeForViewportUnits() const;
+
 protected:
     // Scroll the content via the compositor.
     bool scrollContentsFastPath(const IntSize& scrollDelta);
 
     // Scroll the content by invalidating everything.
     void scrollContentsSlowPath(const IntRect& updateRect);
 
     // These functions are used to create/destroy scrollbars.
     void setHasHorizontalScrollbar(bool);
     void setHasVerticalScrollbar(bool);
@@ skipping 323 matching lines @@
     static const unsigned visualPixelThreshold = 32 * 32;
     if (m_visuallyNonEmptyPixelCount > visualPixelThreshold)
         setIsVisuallyNonEmpty();
 }
 
 DEFINE_TYPE_CASTS(FrameView, Widget, widget, widget->isFrameView(), widget.isFrameView());
 
 } // namespace blink
 
 #endif // FrameView_h